Minerals Engineering 109 (2017) 98–108

Contents lists available at ScienceDirect

Minerals Engineering

journal homepage: www.elsevier .com/ locate/mineng

Behaviour of ilmenite as a gangue mineral in the benzohydroxamicflotation of a complex pyrochlore-bearing ore

http://dx.doi.org/10.1016/j.mineng.2017.02.0090892-6875/� 2017 Published by Elsevier Ltd.

⇑ Corresponding author at: The Robert M. Buchan Department of Mining, Queen’sUniversity, Goodwin Hall, 25 Union Street, Kingston, Ontario K7L 3N6, Canada.

E-mail addresses: 5ceg@queensu.ca (C.E. Gibson), sadan.kelebek@queensu.ca(R. Hansuld), 11rh41@queensu.ca (S. Kelebek), Massoud.Aghamirian@sgs.com(M. Aghamirian).

C.E. Gibson a,b,c,⇑, R. Hansuld a,b, S. Kelebek a,b, M. Aghamirian c

a The Robert M. Buchan Department of Mining, Queen’s University, Goodwin Hall, 25 Union Street, Kingston, Ontario K7L 3N6, CanadabBBA Inc., 630 René-Lévesque Blvd. West, Suite 1900, Montréal, Québec H3B 1S6, Canadac SGS Canada Inc., 185 Concession Street, PO Box 4300, Lakefield, Ontario K0L 2H0, Canada

a r t i c l e i n f o

Article history:Received 25 October 2016Revised 14 February 2017Accepted 21 February 2017

Keywords:FlotationBenzohydroxamic acidIlmenitePyrochloreTitaniumNiobiumSodium hexametaphosphate

a b s t r a c t

One challenge identified in the flotation of niobium bearing minerals with hydroxamates is the recoveryof gangue minerals which can result in concentrate grade dilution. Micro-flotation of single and mixedminerals and bench scale flotation tests on a low-grade complex pyrochlore-bearing ore were conductedto assess the flotation behavior of ilmenite as a gangue mineral in the flotation of pyrochlore using ben-zohydroxamic acid (BHA) as a collector and sodium hexametaphosphate (SHMP) as a dispersant/depres-sant. In micro-flotation, high dosages of BHA resulted in high pyrochlore recovery and low ilmeniterecovery at pH 8. It was observed that the order of addition of SHMP in relation to BHA had a strong effecton pyrochlore recovery, with high recovery maintained only when SHMP was added after BHA. Whenilmenite and pyrochlore were floated in the same system, it was found that reagent addition order playedan important role in selective flotation of pyrochlore. Flotation of pyrochlore was more selective overilmenite when SHMP was added before BHA, similar to a cleaner flotation stage in real-ore flotation.Contrary to micro-flotation results titanium recovery was high (more than 60% TiO2 recovery in mostcases) under similar pulp conditions in bench scale flotation, an indication that to some extent titaniumminerals were recovered by a mechanism other than genuine flotation. Similarly, in mixed mineralmicro-flotation, the recovery of ilmenite increased in the presence of pyrochlore. Two possible scenarios,one physical and the other chemical in nature, have been proposed to explain this observed phenomenon.First, it is possible that moderately floatable titanium mineral particles were recovered in the froth byassociation with highly floatable pyrochlore, particularly at starvation levels of a dispersant (SHMP)through the hydraulic entrainment of fines. The second possibility is that titanium minerals experiencedinadvertent activation in multi-mineral systems, perhaps with metal-hydroxamates as the activatingspecies, forming hydroxamate complexes involving ferric and/or niobium species. This research area isunder further investigation.

� 2017 Published by Elsevier Ltd.

1. Introduction

Pyrochlore (Na,Ca)2Nb2O6(OH,F) is the most economicallyimportant niobium-bearing mineral and is typically upgraded byflotation using an amine-based collector. The pulp pH is main-tained between 5.5 and 7 in the rougher circuit and is graduallydropped to as low as pH 2 in the final cleaner stage (Gibsonet al., 2015a; Bulatovic, 2010; Guimares and Weiss, 2003; Filhoet al., 2002; Oliveira et al., 2001; Gendron et al., 1981). This bene-

ficiation process is reported to be associated with many challenges,including (Ni, 2013; Gibson et al., 2015d):

1. Complicated flowsheets.2. Process sensitivity to the presence of slimes.3. Need for anticorrosive equipment to withstand acidic pulp

conditions.4. Difficulty meeting final concentrate purity specifications.

Globally, there are numerous high grade undeveloped pyro-chlore deposits which cannot be effectively upgraded by flotationbecause ultra fine grinding is required to achieve adequateliberation of highly complexed pyrochlore grains (de OliveiraCordeiro et al., 2011; Bulatovic, 2010; Aral and Bruckard, 2008).Advancement of these deposits is dependent on the development

Table 1XRF Analysis of pyrochlore and ilmenite used in micro-flotation tests.

XRF results Assay (%)

Pyrochlore Ilmenite

Nb 42.8 –Nb2O5 61.2 –SiO2 4.80 0.95Al2O3 0.63 1.01Fe2O3 3.11 31.5MgO 0.07 0.26CaO 9.95 0.14Na2O 2.78 0.12K2O 0.34 0.05TiO2 3.39 61.5P2O5 0.19 0.27MnO 0.06 1.48LOI 3.68 2.06

C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108 99

of beneficiation process that can tolerate slimes and selectivelyrecover fine grained pyrochlore from associated gangue minerals.

Flotation using hydroxamic acids (chelating reagents) as collec-tors has been demonstrated as an effective means to upgrade ultrafine grained material (Pradip and Fuerstenau, 1988). Althoughhydroxamates have historically not been widely used in industryin western countries due to lack of commercial availability, analkyl hydroxamic acid product named ‘IM-50’ is reported to havebeen in commercial use in Russia (former Soviet Union) since the1960s and China since the 1970s (Nagaraj, 1987). Hydroxamicacids are now commercially available worldwide (from reagentmanufacturers such as Cytec), warranting more testwork on realore systems.

Hydroxamates can form complexes with nearly all transitionmetals, although stability is stronger with iron, copper and highlycharged cations than with other transition metals (niobium, tanta-lum, titanium etc.) (Nagaraj, 1987). As a result, selective flotationof transition metals from one another using hydroxamic acids ischallenging and tends to vary depending on the type of hydrox-amic acid used. Factors affecting collector selectivity include bothmineral and chelate solubility; chelate solubility being primarilyaffected by the stability constant (Nagaraj, 1987).

The application of alkyl hydroxamic acid as a collector in flota-tion of pyrochlore-bearing ores at the laboratory scale has beenwell documented (Ni and Liu, 2012a; Gorlovskii et al., 1968). Otherhydroxamic acid types such as benzohydroxamic acid have shownto be effective for pyrochlore recovery through single mineralmicro-flotation studies by Espinosa Gomez et al. (1987) and on realore systems by Gibson et al. (2015a). Independent of the type ofhydroxamic acid, a major issue identified in the flotation of nio-bium bearing minerals with hydroxamates is the recovery of othertransition metal gangue minerals, such as magnetite, hematite,pyrite, ilmenite and rutile (Ni, 2013) which result in concentrategrade dilution.

The present work aims to investigate the flotation of behavior ofilmenite as a gangue mineral in the flotation of pyrochlore usingbenzohydroxamic acid as a collector.

2. Materials and methods

2.1. Mineral sample preparation

A high purity sample of pyrochlore flotation concentrate wasobtained from laboratory and pilot plant flotation testwork con-ducted at SGS in Lakefield, Ontario as this mineral was not avail-able at sufficiently high purity from other sources. In order toensure de-activation/purification of the pyrochlore concentrate, itwas leached with hydrochloric acid at a concentration of 20 g/Lat 20% solids concentration for 4 h at a temperature of 50 �C. Theleach residue was then filtered and washed five times with de-ionized water. The dried leach residue was then heated to 200 �Cfor 45 min to further ensure destruction of any remaining organicson the mineral surface. The purified mineral sample contained�86% pyrochlore assaying 42.8% Nb determined through semi-quantitative XRD and X-ray Fluorescence, respectively. The ilme-nite sample was from mineral storage at the Mining Departmentat Queen’s University. It indicated 35.6% Ti. Subsequent XRD anal-ysis indicated rutile and pseudorutile as minor impurities. Inpreparation for testing, the ilmenite was de-slimed after repeatedultrasonic treatment and decantation/washing at each particle sizeof interest. The XRF results for the pyrochlore concentrate andilmenite samples are presented in Table 1.

Mineral samples were prepared as two size fractions formicroflotation tests. The ‘coarse’ particle size range was -150 lm/+53 lm, and the ‘fine’ particle size range was -53 lm/+20 lm.

Samples were ground using a porcelain mortar and pestle andrequired microsieves.

2.2. Micro-flotation

Micro-flotation tests were carried out in a 70 mL modified Hal-limond tube (Partridge and Smith, 1971). The shaft of the micro-flotation cell was approximately 250 mm long and opened into arounded concentrate launder. A medium porosity piece of frittedglass was located approximately 10 mm above the gas inlet. Aschematic of the micro-flotation cell together with a photo show-ing the cell in action is illustrated in Fig. 1. A Teflon magnetic stir-ring bar from Fisher Scientific was used to suspend mineralparticles in the cell during testing. For all tests, the magnetic stirbar was rotated at a rate of 1000 rpm.

The image in Fig. 1 (right) shows the separation of pyrochlore(brownish froth) from ilmenite (black particles at the bottomremaining mostly unfloatable). It is important to note the presenceof practically barren bubbles in the collection zone separating theconcentrate product and tails after about 30 s into flotation (pH:8.1, BHA: 1.04 � 10�3 M, MIBC: 60 ppm).

For all tests the cell was filled with approximately 40 mL of de-ionized water. The pH in the cell was measured and then adjustedusing sodium hydroxide to reach alkaline conditions. The samplewas conditioned at pH 8 for two minutes. Benzohdyroxamic acidcollector with 99% purity from Alfa Aesar (BHA at 2% by wt.) wasthen added and the sample was conditioned for an additional threeminutes. The BHA dosage ranged from 1 kg/tonne (1.04 � 10�4 M)to 20 kg/tonne, based on weight of the mineral added (1 g). Thesodium hexametaphosphate (or SHMP (NaPO3)6 purchased as‘Calgon’), dosage ranged from 0.5 kg/tonne (1.17 � 10�5 M) to5 kg/tonne. The conditioning period was exactly the same whetherthe SHMP was added before or after the collector. MIBC was addedas a frother in the last minute of conditioning at a rate of 60 mg/L(provided by a tiny drop of pure MIBC from a syringe). Afterconditioning, the air was turned on and adjusted to a flowrate of36 mL/min. Concentrate was collected from the overflow launderfor 1 min while water (de-ionized) was added at the top of the cell(�70 mL/min) to facilitate a continuous overflow of theconcentrate slurry into the launder. Washing water was addedonly to the launder and was not used to change the cell level dur-ing concentrate collection. In the tests involving sodium hexam-etaphosphate (SHMP), its addition was made directly into thecell in powder form.

2.3. Bench scale flotation

A Box-Behnken experimental design was conducted on a low-grade, niobium-bearing carbonatite gravity tailings product to

Fig. 1. Schematic of micro-flotation cell (left) and a photo showing its use during flotation.

100 C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108

examine the main and interaction effects of benzohydroxamic acid(BHA) dosage, pulp temperature, and SHMP dosage. A detailed pro-cedure for this set of tests including head assay and ore samplecharacteristics, experimental run orders, as well as coded anduncoded variable level selection for the experimental design areoutlined by Gibson et al. (2015b). For the convenience of thereader, the flotation feed head assay and experimental conditionsfor the Box-Behnken bench scale flotation tests have been repro-duced in Tables 2 and 3, respectively.

As summarized in the previous work, the flotation tests wereconducted on 2 kg flotation charges in a Denver flotation at a nat-ural pH of 8 (Gibson et al., 2015b). No pulp pH adjustments weremade through conditioning/flotation and the ore was not de-slimed prior to flotation and the feed particle size distributionwas 80% passing 59.3 lm. Four rougher flotation stages were per-formed, each for four minutes in length. Reagents were added inequal quantities in each flotation stage; therefore the results couldbe analysed in each cumulative rougher stage as it was conductedbefore by Nanthakumar and Kelebek (2007).

3. Results and discussion

3.1. Micro-flotation

The mass recovery of pyrochlore and ilmenite (�150/+53 lm)flotation with benzohydroxamic acid at two different concentra-

Table 2Head assay of flotation feed for Box-Behnken bench scale flotation tests (Gibson et al., 20

Sample Assay (%)

Nb2O5 SiO2 Al2O3 Fe2O3 MgO CaO

Flotation Feed 0.25 1.77 0.33 5.04 15.7 31.4

tions is plotted as a function of pH in Fig. 2. It was expected thatpyrochlore and ilmenite flotation recovery with benzohydroxamicacid would be highest between pH 8 and pH 9, near the dissocia-tion constant (pKa) of the reagent, which is given as 8.8(Bonnitcha et al., 2012). Optimal flotation recovery near the pKa

of hydroxamic acid has been attributed to co-adsorption of bothcollector ions and neutral molecules at the mineral surface. Thereaction of meta-hydroxyl complexes at the surface in the presencehydrolyzing metal ions may also increase flotation recovery(Nagaraj, 1987). Based on Fig. 2, pyrochlore demonstrated highfloatability between pH 7 and 8.5; while pyrochlore recoverydropped at pH 9, particularly at low collector dosages. Xu et al.(2016) investigated the flotation of ilmenite with collector2-ethyl-2-hexenoic hydroxamic acid (EHHA) and discovered thatat the single mineral scale, ilmenite recovery was the highest inthe range of pH 8–10. Recovery was significantly lower outsideof this pH range. In the current case, pyrochlore floatability appearsto be more sensitive to alkalinity, as recovery dropped significantlybetween pH 8.5 and 10. Ilmenite recoveries were low regardless ofpH although they reached a maximum around pH 9 at a high col-lector dosage. Under highly alkaline conditions surface reactivity ofthese minerals towards OH- increases, which progressively inhibitscollector action (Liu et al., 2006). It was noted that at an extremepH 12.3; there was no flotation activity for both minerals and thesolution developed a light brownish color, particularly in the caseof ilmenite possible indicative of the precipitation of iron

15b).

Na2O K2O TiO2 P2O5 MnO LOI SUM

0.07 0.07 0.1 4.05 0.56 38.8 98.14

Table 3Operating conditions for Box-Behnken bench scale flotation tests (Gibson et al., 2015b).

Order Box-Behnken level (coded) Actual variable level (uncoded)

Std. Order Run Order Collector (�1) Dispersant (�2) Pulp Temp (�3) BHAa (g/t) Calgona (g/t) Pulp Temp (�C)

1 BB11 �1 �1 0 200 0 402 BB4 1 �1 0 1300 0 403 BB12 �1 1 0 200 400 404 BB9 1 1 0 1300 400 405 BB7 �1 0 �1 200 200 206 BB14 1 0 �1 1300 200 207 BB5 �1 0 1 200 200 608 BB1 1 0 1 1300 200 609 BB8 0 �1 �1 750 0 2010 BB2 0 1 �1 750 400 2011 BB10 0 �1 1 750 0 6012 BB3 0 1 1 750 400 6013 BB6 0 0 0 750 200 4014 BB13 0 0 0 750 200 4015 BB15 0 0 0 750 200 40

a Dosage per rougher (4 roughers total).

0

20

40

60

80

100

7 8 9 10

Mas

s R

ecov

ery

(%)

pH

Pyrochlore - 20 kg/tonne

Pyrochlore - 5 kg/tonne BHA

Ilmenite - 20 kg/tonne BHA

Ilmenite - 5 kg/tonne BHA

Fig. 2. Recovery of pyrochlore and ilmenite (�150/+53 lm) with BHA as a functionof pH.

C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108 101

hydroxamates. This alkaline reactivity is the basis for extractivedecomposition of ilmenite using KOH solutions (Liu et al., 2006).

Flotation tests were performed and repeated three times onilmenite and pyrochlore at pH 8, for high and low collector concen-trations (5 kg/tonne and 20 kg/tonne BHA). Results for therepeated tests are presented in Table 4.

At a collector concentration of 5 kg/t ilmenite recovery wasbetween 9% and 13.5% and pyrochlore recovery was between 87%and 91%. At a collector concentration of 20 kg/t ilmenite recoverywas between 11% and 23% and pyrochlore recovery was between92% and 96%.

Further testing with benzohydroxamic acid was conducted atpH 8 due the high flotation recovery of pyrochlore compared toilmenite regardless of collector dosage and proximity to the pKa.Further, the natural pH of the flotation pulp in bench scale testingrested at around pH 8 and flotation under these conditions elimi-nated the need to modify pH prior to flotation.

Table 4Statistics of repeatability tests for flotation of ilmenite and pyrochlore with BHA.

Ilmenite

20 kg/t BHA 5 kg/t BH

Mean: 16.7 11.8Max: 23.0 13.5Min: 11.0 9.0St Dev: 6.0 2.5

Fig. 3 shows the relationship between mass recovery of pyro-chlore and ilmenite as a function of benzohydroxamic acid concen-tration at pH 8. For this study the particle size range was �150 lm/+53 lm. Pyrochlore recovery was approximately 80% when thebenzohydroxamic acid addition rate was 5 kg/t. Recovery did notincrease significantly when the collector dosage was increasedbeyond 5 kg/t. The recovery of ilmenite reached a plateau at anaddition rate of 2 kg/t BHA and did not increase significantlythereafter.

Lower recovery of pyrochlore observed at high BHA concentra-tions in micro-flotation was due in part to mechanical reasons. Itwas observed that bubbles were sticking to the walls of the cellwhich kept some of hydrophobic particles from floating (fixed atthe walls), preventing them from reporting to the concentrate(Fig. 4).

It is hypothesized that this phenomenon might be related topre-adsorption of active BHA-bearing species on the glass (withor without prior adsorption of some species from pyrochlore), asthe occurrence was not observed when no collector was added tothe system. The observed agglomeration and armouring of tinybubbles by the pyrochlore particles is also important to commenton. This occurred not only in the concentrate but also in the tailsfraction during transfer into a beaker for quantification. Particleagglomeration and armouring of tiny bubbles also occurred withinthe tails. This is indicative of the hydrophobicity of the tailings,although perhaps at a slightly lower level than in the concentrate.These particles possibly remain in the tails fraction because ofmechanical conditions.

Within the particle size range tested, results showed that for agiven concentration of benzohydroxamic acid, pyrochlore wasmore readily floated than ilmenite. For ilmenite and pyrochlore,it is expected that benzohydroxamic acid participates in a com-plexation surface reaction with active metal sites (e.g., Nb, Fe, Ti)at the mineral surface. The tendency of metals to form chelateswith hydroxamates follows the following order (Nagaraj, 1987):

Pyrochlore

A 20 kg/t BHA 5 kg/t BHA

94.0 89.096.0 91.092.0 87.02.8 2.8

0

20

40

60

80

100

0 5 10 15 20 25

Mas

s Re

cove

ry (

%)

BHA Dosage (kg/tonne)

Coarse Pyrochlore (MIX)

Fine Ilmenite (MIX)

Fine Pyrochlore (Single)

Fine Ilmenite (Single)

Fig. 5. Flotation of coarse pyrochlore-fine ilmenite mixture using BHA.

Fig. 4. Incomplete pyrochlore recovery with BHA due to hydrophobic particlessticking to the side of the flotation cell.

0

20

40

60

80

100

0 4 8 12 16 20

Mas

s R

ecov

ery

(%)

BHA dosage (kg/tonne)

Pyrochlore

Ilmenite

Fig. 3. Recovery of pyrochlore and ilmenite as a function of BHA dosage at pH 8.

102 C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108

Fe, Cu, highly charged cations (i.e. Nb5+, Ta5+)

Rare earths and Al

Transition metals, Nb, Ti, V, Mn, Zr, Hf, Ta

Alkaline earth metals

More recently, Parker et al. (2012) experimentally comparedchemical interactions of n-octyl hydroxamate with various coppersulphides such as bornite (Cu5FeS4) and chalcopyrite (CuFeS2), aswell as pyrite as pH 9.5 and above. Formation of multilayer copperhydroxamate was observed on these minerals. Strong chemicalinteraction was evident especially following pre-oxidation andthe hydroxamate was found to be adsorbed on Fe sites of thesecopper sulphide minerals. Co-adsorbed hydroxamic acid and ferrichydroxamate were also observed. Pyrite interacted poorly with thehydroxamate unless it was pre-oxidized. In addition, Yang et al.

(2016) conducted a study on the flotation of wolframite with ben-zohydroxamic acid that concluded the adsorption of benzohydrox-amic acid on high iron wolframite surfaces was higher, as was theflotation recovery. This was attributed to the formation of a newferric product generated from the reaction between benzohydrox-amic acid and iron on the mineral surface.

In reference to the current work, the adsorption of BHA throughinteraction with iron sites rather than titanium on the surface ofilmenite particles is likely a stronger reaction and will result inincreased flotation recovery. Finer grinding may result in increasedsurface exposure of iron (ilmenite) and niobium (pyrochlore), andtherefore increased flotation recovery. These results are in agree-ment with recent investigations which showed the role of iron inpyrochlore flotation (Chelgani et al. (2014, 2013, 2012a, 2012b),Ni and Liu (2012b)).

3.1.1. Mixed mineral micro-flotation testsA series of micro-flotation tests was conducted using 1:1 mix-

tures of pyrochlore and ilmenite at high and low BHA concentra-tions. Two different mixtures were tested:

1. Coarse pyrochlore (�150 lm/+53 lm) and fine ilmenite(�53 lm/+20 lm)

2. Fine pyrochlore (-53 lm/+20 lm) and coarse ilmenite(�150 lm/+53 lm)

The objective of these tests was to understand how particle sizeaffects flotation recovery of the different minerals and how theminerals compete for collector adsorption in flotation as well asthe effect of SHMP on the floatability of single minerals. The resultsare presented in Figs. 5 and 6; the flotation recoveries of pyrochloreand ilmenite in single mineral flotation tests have been includedfor comparison purposes. Note that in the mineral mixture tests,recovery of individual minerals was calculated as a function ofthe initial mass of that mineral following screening of the productsat 270 mesh (53 lm).

Fig. 5 shows that fine ilmenite had an adverse effect on theflotation of coarse pyrochlore when floated in the same environ-ment. At low collector concentration, fine ilmenite out-competedcoarse pyrochlore for collector. At high collector concentrations, anegative effect on coarse pyrochlore by the presence of fine ilme-nite recovery was less significant. These observations highlightout the need for a careful control of collector dosage to starve ilme-nite fines to non-floatability to allow selective recovery of coarsepyrochlore. In single mineral pyrochlore flotation with 5 kg/tBHA, the concentration level for starvation of ilmenite was likelymet. However when fine ilmenite was present in the flotation sys-tem and competed with pyrochlore for collector adsorption, there

0

20

40

60

80

100

0 5 10 15 20 25

Mas

s R

ecov

ery

(%)

BHA Dosage (kg/tonne)

Fine Pyrochlore (MIX)

Fine Pyrochlore (Single)

Coarse Ilmenite (MIX)

Coarse Ilmenite (Single)

Fig. 6. Flotation of fine pyrochlore-coarse ilmenite mixture using BHA.

0

20

40

60

80

100

0 1 2 3 4 5

Mas

s R

ecov

ery

(%)

SHMP dosage (kg/tonne)

Pyrochlore: SHMP before BHA

Pyrochlore: SHMP after BHA

llmenite: SHMP before BHA

Ilmenite: SHMP after BHA

Fig. 7. Effect of SHMP on flotation of pyrochlore and ilmenite as single minerals(�150 lm/+53 lm) according to order of addition with respect to BHA addition.

C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108 103

was no longer sufficient collector available to recover both ilmeniteand the coarse pyrochlore. At a collector concentration of 20 kg/t, itis feasible that there was sufficient collector available to recovercoarse pyrochlore even in the presence of fine ilmenite. Decreasedpyrochlore recovery observed in the mixture test compared to thesingle mineral test at 20 kg/t BHA is likely within the range ofexperimental variability.

The case for behaviour of coarse ilmenite mixed with fine pyro-chlore is given in Fig. 6. Ilmenite recovery was greater when floatedtogether with the fine pyrochlore at both low and high collectordosage levels. The recovery of fine ilmenite was higher whenfloated together with pyrochlore than when floated as a singlemineral for three of four conditions tested. This indicated the pos-sibility of inadvertent activation of ilmenite by pyrochlore. It issuggested that the high flotation recovery of ilmenite observed inbench scale flotation (as will be discussed in subsequent sections)may be partly related to the same phenomenon of inadvertent acti-vation. Of course, it is also possible that small amounts of fine ilme-nite were recovered through entrainment with the highly floatablepyrochlore particles.

It appears that the possibility of inadvertent activation is statis-tically significant rather than attributing the trend in these resultsto merely experimental error. The percentage of difference in somecases is greater than that observed in repeatability tests (Table 4).In bench scale testing, the ore sample in its entirety (i.e. pyrochloreand all gangue minerals) is processed together and there arenumerous mineral-mineral interactions not only during condition-ing/flotation, but also during grinding which enable evolution andtransfer of active species from mineral to mineral as well asthrough the grinding media. The aqueous phase should play a roleas a medium in the transfer of activating species considering theuse of high collector dosage levels (5–20 kg/tonne) and possiblythrough complexation reactions.

3.1.2. Effect of SHMP in micro-flotation: Single mineral and mixedmineral cases

The impact of SHMP was tested on flotation recovery of pyro-chlore and ilmenite as single minerals and as 1 to 1 mixtures.Fig. 7 shows the single mineral recoveries as a function of SHMPdosage for both minerals, with respect to the order of its additionin relation to BHA. In both cases, pyrochlore recovery decreasedwith an increase in SHMP dosage. Recovery of ilmenite, whichwas much lower than that of pyrochlore, also decreased withSHMP dosage but the reduction was not as significant as in the caseof pyrochlore. This may be because the level of ilmenite recoverywas already low and any further decrease was marginal due tophysical constraints related to the small-scale of testing. From afundamental perspective, the difference in function of BHA and

SHMP is mainly related to their adsorption mechanism. Sodiumhexametaphosphate is a source of polyanionic species (Bulatovic,2007). As such, it can act as a dispersant in aqueous processing sys-tems through adsorption of its polyanions. It can also act as adepressant for gangue minerals associated with pyrochlore. In gen-eral, such interactions are typical of weak adsorption, eventuallyleading to formation of relatively soluble surface complexes(Hatch and Rice, 1939; Ni and Liu, 2013). According to the currentresults, SHMP can act as a pyrochlore depressant in flotation withBHA. This suggests that the dosage of SHMP needs to be closelycontrolled in flotation circuits.

A striking feature of the results presented in Fig. 7 is the effect ofreagent addition order. When SHMP was added before BHA, thedepression effect on pyrochlore was quite severe compared towhen it was added after BHA. The same effect of the addition orderwas also visible on ilmenite, but to a lesser extent due mainly tothe fact that recovery level was already low. It can be hypothesizedthat when SHMP is adsorbed on the surface of such minerals, it sta-bilizes the hydrophilicity of that surface through hydrogen bond-ing. Since it is a large molecule with 18 oxygen atoms ((NaPO3)6),it is capable of forming multiple hydrogen bonds with water.Therefore the barrier between the mineral surface and collectorspecies of BHA is thicker and denser. When BHA is used beforeSHMP, the hydrogen bonding capability of the surface is consider-ably blocked and the depressing action of SHMP is limited.

The case for the binary mixture of pyrochlore and ilmenite isgiven in Fig. 8, where the effect of SHMP at 5 kg/tonne is comparedfor two levels of BHA dosage at 5 kg/tonne and 20 kg/tonne. It wasobserved that the order of reagent addition had the same effect onflotation behavior in the pyrochlore-ilmenite mixed mineral sys-tem. However, recovery levels were somewhat different in themixed mineral system compared to the single mineral system. Pyr-ochlore recovery in the absence of SHMP was similar at about 80%and was reduced to 17% following SHMP addition ahead of BHA.When the SHMP was added after BHA, the recovery of pyrochloredid not drop to the same extent. When the dosage of BHA wasincreased to 20 kg/tonne, the depressing action of SHMP on pyro-chlore was less significant as the collector/depressant ratio wasmore favourable. The relative effect of SHMP on the flotation beha-viour of ilmenite is similar. Table 5 shows the variation of the pyr-ochlore/ilmenite ratio in the concentrate with respect to use ofSHMP. The ratios were consistently higher for a larger BHA/SHMPratio (high BHA dosage, with SHMP dosage held constant) regard-less of the order of addition, indicating that pyrochlore selectivityis favoured by the relative dosage of BHA. It is also clear that thepyrochlore/ilmenite ratio is highest when SHMP is added afterBHA. The practice of adding a modifier (such as SHMP) after collec-tor addition in flotation corresponds to a ‘‘cleaners” stage, where

0

20

40

60

80

100

BHA, No SHMP

SHMP before BHA

SHMP after BHA

Mas

s R

ecov

ery

(%)

5 kg/tonne BHA20 kg/tonne BHA

0

5

10

15

20

25

30

35

40

BHA, No SHMP

SHMP before BHA

SHMP after BHA

Mas

s R

ecov

ery

(%)

5 kg/tonne BHA20 kg/tonne BHA

Fig. 8. Effect of SHMP (at 5 kg/tonne) on flotation of pyrochlore (�53 lm/+20 lm, left) and ilmenite (�150 lm/+53 lm, right) in their 1 to 1 mixtures according to order ofaddition with respect to BHA addition.

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Rec

over

y (%

TiO

2)

Recovery (% Nb2O5)

BB1BB2BB3BB4BB5BB6BB7BB8BB9BB10BB11BB12BB13BB14BB15

Fig. 9. TiO2 recovery as a function of Nb2O5 recovery in Box-Behnken rougherflotation tests.

104 C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108

an upgraded stream originating from a primary flotation stage hasalready been treated with collector. Thus, these results have rele-vance to relative effects of reagents in flotation practice (e.g. selec-tivity function in the cleaners).

3.2. Bench scale flotation

Grade-recovery curves and assessment of the interaction effectsof the parameters tested in the Box-Behnken experiment havebeen detailed for niobium by Gibson et al. (2015b) and for variousgangue components by Gibson et al. (2015c).

A plot of titanium dioxide recovery as a function of niobiumpentoxide recovery is presented in Fig. 9. A ‘Line of No Selectivity’has been included in the plot to clearly illustrate that the selectiveflotation of niobium over titanium is minimal. In fact, for mosttests conducted there is a near perfect linear correlation betweenniobium recovery and titanium recovery. While it is known thatpyrochlores are complex oxides and can contain titanium in theircrystal structure (Chelgani et al. (2012a), XRD analysis of the flota-tion concentrate (Section 3.2.1) shows the presence of ilmenite as adistinct mineral phase. Therefore it is unlikely that the linear trendobserved Fig. 9 can be wholly attributed to the presence of tita-nium within the pyrochlore structure.

Fig. 9 suggests that niobium and titanium minerals have anearly equal affinity for, and therefore equal flotation response,to the collector. However, small scale flotation testing of ilmeniteat pH 8 has revealed that this is not the case, leaving two possibil-ities for the co-dependent recovery of niobium and titanium. Aspreviously mentioned, the first possibility is that titaniumminerals(mainly ilmenite in this ore) are subject to inadvertent activationin real ore flotation where the flotation pulp can act as a mediumto transfer soluble species (such as iron species) which may con-tribute to the increased recovery of titanium oxides. Investigationsby Parker et al. (2012) indicated multiple species on coppersulphides forming hydrophobic layers, which included not onlycopper hydroxamate and hydroxamic acid, but also ferric

Table 5Effect of order of addition of SHMP on pyrochlore (�53 lm/+20 lm)/ilmenite(�150 lm/+53 lm) ratio recovered in flotation.

Reagent conditions Pyrochlore to ilmenite ratio in concentrate

5 kg/tonne BHA 20 kg/tonne BHA

BHA, No SHMP 3.7 4.1SHMP before BHA 1.7 2.2SHMP after BHA 5.0 6.0

hydroxamate. Jordens et al. (2014) reported that adsorption of fer-rous and ferric iron species caused positive shifts in the zeta poten-tial of allanite (a rare earth oxide mineral) providing active sites forstronger interactions with benzohydroxamic acid. Considering thatthere are multiple sources of iron species in process streamsincluding the grinding mill and media, they are often an integralpart of process chemistry. It is possible that activating species forgangue minerals such as ilmenite in the present case are in theform of metal-hydroxamates, which may have formed hydroxam-ate complexes involving ferric and possibly niobium species (aresearch area under further investigation). Assuming that themechanism does not significantly involve locked particle recovery,the second possibility is that titanium minerals, which exhibitsome floatability as has been noted in earlier research on flotation(Gaudin, 1957; Klassen and Mokrousov, 1963), are also recoveredby physical association among strongly hydrophobized pyrochloreparticles and bubbles forming clusters, a phenomena given recentattention by Ata and Jameson (2005). Another possibility of courseis hydraulic entrainment mechanism, which may contribute torecovery of gangue in the fines particle size range.

3.2.1. Mineral balanceFlotation products from test BB6 (Fig. 9), one of the three centre

point runs (in terms of coded variables: BHA = 0 level, SHMP = 0

C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108 105

level, pulp temperature = 0 level), was analysed by semi-quantitative X-ray diffraction (XRD). The flotation products fromthis particular test were selected as they yielded high niobiumrecovery and the highest niobium upgrade of all Box-Behnken runsconducted. A full mineralogical balance for all significant mineralsin the system is reported by Gibson et al. (2015c). Based on analy-sis of the rougher concentrates and final tails, it appears that ilme-nite underwent rapid and very high recovery. The estimatedcumulative mineral recovery of only pyrochlore, ilmenite and cal-cite (as a means of comparison) as a function of mass recovery arepresented in Fig. 10. The error bar (±25%) is a conservative repre-sentation of relative accuracy of the semi-quantitative XRD resultsbased on XRD accuracy studies conducted by Brime (1985) andSturges and Harrison (1989). Comparing the high recovery(�90%) of ilmenite to the overall elemental TiO2 recovery of72.7% (after 4 stages) in BB6 in Fig. 9, it is evident that titaniummust be present in another mineral, which is not being recoveredto the concentrate.

It is plausible that a portion of titanium is present in the form ofother minerals such as rutile, which would account for some of thediscrepancy between titanium mineral and elemental recovery tothe niobium concentrate. Since semi-quantitative XRD analysishas a significant inherent error in the analysis of minor compo-nents it is probable that ilmenite recovery was even lower. Simi-larly, pyrochlore recovery in Fig. 10 was reported to be about60% after two rougher flotation stages, while more reliable elemen-tal analysis by XRF puts niobium recovery closer to 90% after tworougher flotation stages. This discrepancy is also likely in partdue to the lack of accuracy of semi-quantitative XRD analysis incomplex mineralogical systems.

3.2.2. Significant factors (niobium and titanium Recovery)Table 6 outlines the statistically significant factors that affected

the recovery of niobium and titanium minerals.At the 95% confidence interval, temperature (‘C’) showed no sta-

tistically significant effect on either niobium or titanium recovery.The probable reason for this was attributed to the fact that therequired concentration of BHA to show its overall collecting powerthrough its predominant chemisorption mechanism in this flota-tion system was attainable within its solubility limit at ambienttemperature (Gibson et al., 2015b). The interaction term ‘AB’ showsthe positive interaction effect of collector and SHMP on the recov-ery of both titanium and niobium. The ‘-A2’ term defines the curva-ture of the surface plots presented in Fig. 11.

IlmenitePyrochloreCalcite

100

80

60

40

20

2 4 6 8 10 12 14

Mass Recovery (%)

Min

eral

Rec

over

y (%

)

0

Fig. 10. Mineral recovery in centre point run BB6 (A = 0; B = 0; C = 0 level) forpyrochlore, ilmenite and calcite after Gibson et al. (2015c).

3.2.3. Titanium recovery (Rougher 1)Surface plots for titanium recovery after the first stage of

rougher flotation are presented in Fig. 11. Beginning in the firststage of rougher flotation the significant factors from Table 6(including the positive effect of collector, the negative interactiveeffect of collector and SHMP, and the negative exponential effectfor the collector dosage which defines the curvature of the surfaceplots) are the same for both niobium and titanium. Moreover, thesurface plots for titanium recovery in Fig. 11 after one rougherflotation stage are nearly identical in terms of shape and curvatureto those reported earlier for pyrochlore (Gibson et al., 2015b).However, from a quantitative point of view, some differences arenoticeable. One difference is the relative drop in recovery withdecreasing dosage of BHA with respect to temperature, whichwas greater for ilmenite (Fig. 11B). The other difference is relatedto the sensitivity of ilmenite recovery to the dosage of SHMP(referred to as Calgon in figures). The relative drop in ilmeniterecovery with increasing dosage of this dispersant/depressant issomewhat greater at higher temperature. Both of these quantita-tive effects make sense in view of intended functionality of thesereagents for ilmenite as a gangue mineral.

The fact that the statistically significant factors are exactly thesame for both niobium and titanium (Table 6) and flotation ofthe latter is nearly complete suggests that the recovery mechanismof both minerals have common features. As discussed previously,this can be a manifestation of association between the two miner-als, or their somewhat similar surface chemistry due to inadvertentactivation or both aspects acting together. According to results ofsingle mineral experiments representing a fully liberated case,one can conclude that the flotation response of ilmenite in mix-tures is limited due to a genuine lack of surface chemical activity.More detailed research is required in this area combining the liber-ation analysis and surface chemical responses.

3.2.4. Titanium recovery (Rougher 1–2)Surface plots for titanium recovery after the first stage of

rougher flotation are presented in Fig. 12. After two rougher flota-tion stages, increased addition of SHMP had a statistically signifi-cant negative effect on titanium recovery, but not on niobiumrecovery. The negative effect of SHMP addition rate on titaniumrecovery is clearly visible in comparison with the first stage(Fig. 11C). This simply points to the increased dispersion/depres-sion effects on titanium minerals with higher addition rates ofSHMP. Considering that these results represent cumulative recov-eries, it can be concluded that onset of the selective negativeimpact of SHMP on ilmenite recovery occurred in the individualsecond stage. Thus, this technique of stage wise analysis of flota-tion by statistical design of experiments (Nanthakumar andKelebek, 2007) is a helpful diagnostic statistical approach charac-terizing the evolution of reagent effects from a kinetics point ofview.

It is worth noting that SHMP is a multifunctional reagent and itcan act differently depending on the flotation system in which it is

Table 6Statistically significant factors at the 95% confidence level for Nb2O5 recovery andTiO2 recovery after each of the four rougher flotation stages.

Combinedconcentrates

Flotation time(min.)

Significant factors

Recovery (%Nb2O5)

Recovery (%TiO2)

Rougher 1 4 A, AB, -A2 A, AB, -A2

Rougher 1–2 8 A, AB, -A2 A, -B, AB, -A2

Rougher 1–3 12 A, -B, -A2 A, -B, AB, -A2

Rougher 1–4 16 A, -B, AB, -A2 A, -B, AB

A = BHA dosage, B = Calgon dosage, C = Pulp temperature.

Fig. 11. Interaction effects of variables on TiO2 recovery after a single rougher flotation stages. For each surface plot, the third variable is held constant at the zero level(coded).

106 C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108

used. A study conducted by Ding et al. (2007) demonstrated thatSHMP acted as an effective apatite depressant in the flotation ofrutile by selectively dissolving Ca2+ on the surface of apatite, reduc-ing surface cation points and lessening zeta potential; flotation ofrutile as a titanium oxide as a single mineral was not affected bySHMP addition in the presence of an alkyl-amino-bismethylenephosphoric acid as a collector. Ni and Liu (2013) investigated theadsorption of SHMP on the surface of calcite. The authors foundthat SHMP formed a complex with calcium on the surface of cal-cite, preventing the adsorption of an alkyl hydroxamic acid. Inthe present batch flotation system, the mechanism of the observedilmenite depression is not clear. It may involve an adsorption basedpassivation of the ilmenite surface by SHMP. However, an indirectmechanism involving other types of gangue minerals such as cal-cite interlocked with ilmenite (in the form of middlings) cannotbe ruled out.

These aspects require a specific surface chemical investigationfocusing on details of ilmenite-SHMP interactions under the influ-ence of relevant collectors. The negative contribution of SHMP con-tinued to have a significant effect on titanium recovery through theremaining stages of rougher flotation. It was not until the final twostages of rougher flotation that niobium recovery experienced asimilar negative SHMP effect. This effect has been attributed tothe depression of middlings particles by a similar mechanism asproposed above by Gibson et al. (2015b).

4. Summary and conclusions

Micro-flotation on single and mixed minerals and bench scaleflotation tests on a low-grade complex pyrochlore-bearing orewere conducted with the objective to assess the flotation behaviorof ilmenite as a gangue mineral in the flotation of pyrochlore withbenzohydroxamic acid as a collector and sodium hexametaphos-phate as a dispersant/depressant.

Considering the poor floatability of ilmenite observed in micro-flotation tests under similar pulp conditions to those tested in theBox-Behnken design bench scale flotation tests, it appears that inreal ore systems, titanium minerals were recovered at least in partby a mechanism other than genuine flotation. One possible sce-nario is that moderately floatable titanium mineral particles wererecovered in the froth by physical association with highly floatablepyrochlore, particularly when starvations levels of a dispersant(SHMP) were added to the system. Another possibility for recoveryof ilmenite is an inadvertent activation by metal ions (e.g., involv-ing iron and niobium) or their hydroxamate complexes.

In micro-flotation of single minerals it was observed that theorder of addition of SHMP in relation to BHA had a strong effecton pyrochlore recovery. High pyrochlore recovery was achievedonly when a high dosage of SHMP was added after BHA. The impactof SHMP addition on ilmenite recovery was less notable mainlydue to the fact that ilmenite recovery was already quite low. In a

Fig. 12. Interaction effects of variables on TiO2 recovery after two rougher flotation stages. For each surface plot, the third variable is held constant at the zero level (coded).

C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108 107

mixed pyrochlore-ilmenite micro-flotation system, it was foundthat reagent addition order played an important role in the selec-tive flotation of pyrochlore over ilmenite. Improved selectivitywas observed when SHMP was added before BHA, similar to a clea-ner flotation stage in real-ore flotation.

In bench scale flotation, as SHMP levels were increased titaniumrecovery decreased, showing that increased dispersion may helpminimize entrainment. In addition, high dosages of SHMP mayhave contributed to the depression of titanium-calcite middlingsparticles, also explaining the significant negative effect of SHMPaddition rate on titanium recovery. These results suggest thatwhile SHMP can improve selective flotation of pyrochlore overilmenite, it can also act as a pyrochlore depressant in flotation withBHA and that the dosage of SHMP needs to be closely controlled inflotation circuits.

In most cases, mixed-mineral micro-flotation tests showed thatilmenite recovery increased in the presence of pyrochlore. Thisobservation may also be the result of ilmenite entrainment withhighly floatable pyrochlore; however it also raises the possibilitythat titanium minerals experience inadvertent activation in thepresence of pyrochlore and in the real ore system, potentially withmetal-hydroxamates as the activating species which may haveformed hydroxamate complexes involving ferric and/or niobiumspecies. Further surface characterization of ilmenite is requiredto determine if inadvertent activation is occurring and if so, themechanism of activation. Thorough understanding of the meansby which titanium minerals are recovered to the niobium concen-

trate in flotation with benzohydroxamic acid will assist in rejectionof unwanted gangue components.

Acknowledgements

The authors would like to acknowledge SGS Canada (Lakefield)for their ongoing support of this research. The authors would alsolike to acknowledge funding for C.E. Gibson from SGS Canada, theRobert M. Buchan Department of Mining, and Ontario GraduateScholarships (OGS).

References

Aral, H., Bruckard, W.J., 2008. Characterisation of the Mt Weld (Western Australia)niobium ore. Min. Proc. Extract. Metall. 117, 193–204.

Ata, S., Jameson, G.J., 2005. The formation of bubble clusters in flotation cells. Int. J.Miner. Process. 76, 123–139.

Bonnitcha, P.D., Kim, B.J., Hocking, R.K., Clegg, J.K., Turner, P., Neville, S.M., Hambley,T.W., 2012. Cobalt complexes with tripodal ligands: implications for the designof drug chaperones. Dalton Trans. 41, 11293–11304.

Bulatovic, S.M., 2010. Flotation of niobium/tantalum ores. In: Bulatovic, S.M. (Ed.),Handbook of Flotation Reagents: Chemistry, Theory and Practice – Volume 2:Flotation of Gold, PGM and Oxide Minerals. Elsevier B.V., pp. 111–125.

Brime, C., 1985. The accuracy of X-ray diffraction methods for determining mineralmixtures. Mineral. Mag. 49, 531–538. September.

Chelgani, S., Hart, B., Beisigner, B., Marois, J., Ourriban, M., 2014. Pyrochlore surfaceoxidation in relation to matrix Fe composition: a study by X-ray photoelectronspectroscopy. Miner. Eng. 55, 165–171.

Chelgani, S., Hart, B., Marois, J., Ourriban, M., 2013. Study the relationship betweenthe compositional zoning of high iron content pyrochlore and adsorption ofcationic collector. Miner. Eng. 46–47, 34–37.

108 C.E. Gibson et al. /Minerals Engineering 109 (2017) 98–108

Chelgani, S., Hart, B., Marois, J., Ourriban, M., 2012a. Study of pyrochlore surfacechemistry effects on collector adsorption by TOF-SIMS. Miner. Eng. 39, 71–76.

Chelgani, S., Hart, B., Marois, J., Ourriban, M., 2012b. Study of pyrochlore matrixcomposition effects on froth flotation by SEM-EDX. Miner. Eng. 30, 62–66.

de Oliveira Cordeiro, P.F., Brod, J.A., Palmieri, M., Gouveia de Oliveira, C., Barbosa, E.S., Santos, R.V., 2011. The Catalao I niobium deposit, central Brazil: resources,geology and pyrochlore chemistry. Ore Geol. Rev. 41 (1), 112–212.

Ding, H., Lin, H., Deng, Y., 2007. Depressing effect of sodium hexametaphosphate onapatite in flotation rutile. J. Univ. Sci. Technol. Beijing 14, 200–203.

Espinosa Gomez, R., 1987. Recovery of Pyrochlore From Slimes Discarded at Niobecby Column Flotation PhD thesis. McGill University, Montreal.

Filho, A.I., Riffel, B., de Faria Sousa, C.A., 2002. Some aspects of the mineralogy ofCBMM niobium deposits and pyrochlore ore processing. In: NiobiumProceedings of the International Symposium, Orlando, Fl, USA, p. 13.

Gaudin, A.M., 1957. Flotation. McGraw-Hill, New York.Gendron, L., Biss, R., Rodrigue, M., 1981. Underground mining and pyrochlore ore

processing at Niobec mine, Quebec, Canada. In: Niobium Proceedings of theInternational Symposium. The Metallurgical Society of AIME, San Francisco,California, pp. 79–113.

Gibson, C., Kelebek, S., Aghamirian, M., 2015a. Flotation of niobium oxide minerals:a review of relevant literature and the current state of industrial operations. Int.J. Miner. Process. 137, 82–97.

Gibson, C.E., Kelebek, S., Aghamirian, M., Yu, B., 2015b. Flotation of fine grainedpyrochlore from low grade carbonatite gravity tailings using benzohydroxamicacid. Miner. Eng. 71, 97–104.

Gibson, C.E., Kelebek, S., Aghamirian, M., 2015c. Application of Box-Behnken designto modelling of iron-bearing gangue recovery in hydroxamate flotation ofpyrochlore. In: MetSoc Conference of Metallurgists 2015. Toronto, Ontario,Canada.

Gibson, C.E., Kelebek, S., Aghamirian, M., 2015d. Challenges in niobium flotation,47th Annual Canadian Mineral Processors Conference 2015. In: 47th AnnualCanadian Mineral Processors Conference 2015. Ottawa, Ontario, Canada.

Gorlovskii, S.I., Eropkiny, I., Koval, E.M., Strelstin, V.G., Khobotova, N.P., Shtchukina,E.E., 1968. Improvement in concentration technology of some rare metals ores⁄based on taking advantage of complexing alkyl hydroxamic acids pecularities ofaction. In: VIII International Mineral Processing Congress, Leningrad, pp. D3–D9.

Guimares, H.N., Weiss, R.A., 2003. The Complexity of the Niobium Deposits in theAlkaline Ultramafic Intrusions Catalão I and II – Brazil. Mineração Catalão, SãoPaulo, SP, Brasil.

Hatch, G.B., Rice, O., 1939. Surface-active properties of haxametaphosphate. Ind.Eng. Chem. 31 (1), 51–57.

Jordens, A., McCarthy, S., Waters, K.E., 2014. The effect of activating ions on theadsorption of a benzohydroxamic acid collector onto a rare earth silicate. In:Conference of Metallurgists Proceedings, Canadian Institute of Mining,Metallurgy and Petroleum.

Klassen, V.I., Mokrousov, V.A., 1963. An Introduction to the Theory of Flotation.Butterworths, London.

Liu, Y.M., Qi, T., Chu, J.L., Tong, Q., Zhang, Y., 2006. Decomposition of ilmenite byconcentrated KOH solution under atmospheric pressure, International. J. Min.Proc. 81, 79–84.

Nagaraj, D.R., 1987. Reagents in Mineral Technology. In: Moudgil, B.M.,Somasundaran, P. (Eds.), Surfactant Science Series, vol. 27. Marcel Dekker,New York, NY.

Nanthakumar, B., Kelebek, S., 2007. Stagewise analysis of flotation by factorialdesign approach with an application to the flotation of oxidized pentlandite andpyrrhotite. Int. J. Miner. Process. 84, 192–206.

Ni, X., 2013. Direct Flotation of Niobium Oxide Minerals From Carbonatite NiobiumOres. University of Alberta, Edmonton.

Ni, X., Liu, Q., 2013. Adsorption behavior of sodium hexametaphosphate onpyrochlore and calcite. Can. Metall. Q. 52, 473–479.

Ni, X., Liu, Q., 2012a. Developing flotation reagents for niobium oxide recovery fromcarbonatite Nb ores. Miner. Eng. 36–38, 111–118.

Xiao, X., Liu, Q., 2012b. The adsorption and configuration of octyl hydroxamic acidon pyrochlore and calcite. Coll. Surf. A Physicochem. Eng. Asp. 411, 80–86.

Oliveira, J.F., Saraiva, S., Oliveira, A., 2001. Technical note kinetics of pyrochloreflotation from Araxá mineral deposits. Miner. Eng. 14, 99–105.

Parker, G.K., Buckley, A.N., Woods, R., Hope, G.A., 2012. The interaction of theflotation reagent, n-octanohydroxamate, with sulfide minerals. Miner. Eng. 36–38, 81–90.

Partridge, A.C., Smith, G.W., 1971. Technical notes, Small-sample flotation testing: anew cell. Trans. IMM., 199–200

Pradip, Fuerstenau, D.W., 1988. Alkyl hydroxamates as collectors for the flotation ofbastnaesite rare earth ores. In: Bautista, R.G., Wong, M.M. (Eds.), Rare Earths-Extraction, Preparation and Application. AIME/TMS, Warrendale, Pennsylvania,pp. 57–70.

Sturges, W.T., Harrison, R.M., 1989. Semi-quantitative x-ray diffraction analysis ofsize fractionated atmospheric particles. Atmos. Environ. 23 (5), 1083–1098.

Yang, S., Peng, T., Li, H., Feng, Q., Qiu, X., 2016. Flotation mechanism of wolframitewith varied components Fe/Mn. Miner. Process. Extr. Metall. Rev. 37, 34–41.

Xu, H., Zhong, H., Tang, Q., Wang, S., Zhao, G., Liu, G., 2016. A novel collector 2-ethyl-2hexenoic hydroxamic acid: flotation performance and adsorption mechanismto ilmenite. Appl. Surf. Sci. 353, 882–889.