annual report 2006

Technical Review

Technical Review

annual report 2006

Gold industryThe monitoring of cyanide to ensure compliance with best practice codes is continuing within the gold mining industry. Mintek has developed the expertise to assist in this regard and is contracted by AngloGold Ashanti to routinely monitor relevant effluents from all of its mines in Africa. Mintek participated in ICMI-based gap audits at AngloGold Ashanti’s Sadiola, Yatela, and Morila mines in Mali, and at Gold Fields’ Beatrix plant in South Africa. Audits at Navachab (Namibia), Geita (Tanzania), Iduapriem and Bibiani (Ghana), and Siguiri (Guinea) are scheduled. An audit of Sasol’s sodium cyanide plant at Sasolburg and of Sasol Infrachem for compliance with the ICMI Producers’ and the ICMI Transportation Code respectively has also been scheduled for May 2006, and will be conducted under Mintek team leadership. Monitoring and auditing of sites for compliance with international codes has resulted in Mintek being recognised as a centre of expertise, and requests for related work are increasing.

Cyanide mass balancing and speciation over mine sites has resulted in major advances in the modelling of HCN evaporation. The work is supported by the DTI through the THRIP mechanism and by AngloGold Ashanti, who seconded one of their engineering staff to Mintek to carry out an MSc project on cyanide volatilisation and to develop a cyanide mass balance model for their operations. The project was successfully completed, and the company is implementing the mass balance model at test sites. Further work will be carried out to extend the model to include precipitation, chemical degradation and ultraviolet dissociation. Two BTech projects have also been started on the biodegradation of cyanide and cyanide complexes.

At the request of Office des Mines d’Or de Kilomoto (OKIMO), Mintek conducted a preliminary assessment of potential resources contained in the tailings deposits of Durba and Kalimva in the eastern DRC. The work was undertaken In conjunction with EPC (formerly Grinaker LTA), who are assessing the feasibility of refurbishing the original leaching and cementation plant.

A comprehensive metallurgical test programme was carried out on samples from a deposit in Tanzania consisting of comminution and flotation, leaching, and cyanide destruction. Ongoing work was conducted to optimise the leaching conditions at the Gallery Gold’s mine in Botswana, as well as regular control testwork on plant samples for EPC. Metallurgical testwork and plant simulations were done to provide data for the bankable feasibility studies for Aflease Gold’s new Modder East plant on the Witwatersrand, and for AngloGold Ashanti’s Sadiola project in Mali, and leaching testwork carried out for the Navachab mine in Namibia.

Project AuTEK is a joint initiative between Mintek and the three major South African gold mining houses to develop new industrial uses of gold in the fields of catalysis, nanotechnology and biomedical applications.

The AuTEK catalysis programme continued product development with potential end-users. Production of gold-based catalysts has been scaled up to commercial 20 kg batches, which are being promoted as custom made catalysts with assistance of the World Gold Council. Mintek is collaborating with an international catalyst producer to evaluate the potential for commercial production of gold-based catalysts at the tonnage scale for air purification and

Part of the original gold-recovery plant at Durba in the eastern DRC, which is still operating using a flowsheet comprising milling, gravity separation, and amalgamation.

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Sampling of tailings at Durba, eastern DRC, by auger drilling.

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Technical Review

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Technical Review

other industrial applications. R&D in the new field of photocatalysis was started during 2005, with the focus on the photodegradation of certain organic pollutants. The addition of gold to traditional metal-oxide photocatalyst materials increases their activity, extends their light adsorption capabilities into the visible region, and enables the catalysis of novel reactions.

In the fuel cell programme, the PureAuroH2 system to remove CO levels from the hydrogen feedstock has been patented. The technology, which was tested at Johnson Matthey’s laboratories in the UK during an exchange visit by a member of the AuTEK team, removes carbon monoxide from hydrogen at room temperature from an initial 10-2000 ppm to less than 1 ppm. Mintek is seeking commercial partners to help develop this innovative technology for use in purifying the onboard-generated hydrogen feed to fuel cells.

A collaborative gold nano-biolabelling R&D project at University of Liverpool has won awards both locally and abroad. AuTEK nanoscale R&D has broadened to involve five local universities. Two PhD projects on nanoparticle structures and

advanced biolabel development have been started at the University of Zululand, and work in the fields of sensors and biosynthesis was initiated at the University of Johannesburg and Rhodes University respectively. A PhD project on nanostructure modelling and simulation will be completed in the second half of 2006.

At the end of the period under review, Mintek commissioned a dedicated nano-characterisation laboratory equipped with a R4.5 million scanning probe microscope (SPM) funded by the Department of Science and Technology (DST) and a high-resolution scanning electron microscope (HRSEM) with a resolution down to 2 nm. Mintek is the only organisation on the African continent with such a comprehensive capacity for nanoscale research. The SPM comprises two main components - a MultiMode and an EnviroScope. One of the modes on the MultiMode allows mechanical properties such as hardness to be measured on the nanometre scale. In the conventional configuration, the MultiMode can measure the electrical and magnetic properties on the surface of a material. The EnviroScope component allows the SPM technique to be carried out in different environments, for example in a vacuum, gases, or liquids, and can also be configured to perform electrochemical investigations on very small areas.

The AuTEK Biomedical Programme focuses on creating new types of metal-based chemotherapeutic agents for health concerns in southern Africa, with the emphasis on those diseases where there is a clear need for improved medicine, such as cancer, malaria, and HIV/AIDS. Research activities are centred mainly on aspects of synthetic gold chemistry and pharmacology, encompassing important aspects of drug design, and the programme involves collaboration with seven local and ten international universities. More than 140 novel gold-based compounds have been screened against various tumour cell-lines, and a number of highly potent classes of compounds have been identified. Extensive structural modification of identified compounds has resulted in higher tumour selectivity and efficacy, and a submission towards a patent application is in progress. Investigations are now aimed at understanding the cytotoxicity and the mechanism by which these compounds affect cancer cells, as well as establishing the relationships between chemical structure and pharmacokinetic properties.

The anti-malarial programme, which began in 2005, is exploring the efficacy of gold complexes on various levels, through the synthesis of bioactive ligand systems and their complexation to gold. A range

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Preparation of in vitro cell

assays by multiple dilution

in the AuTEK Biomedical screening

laboratory.

The high-resolution scanning electron

microscope in Mintek’s nano-

characterisation laboratory.

annual report 2006

Technical Review

of compounds has been subjected to antimalarial screening, and a single compound has been shown to have antimalarial activity against both CQ-sensitive and CQ-resistant strains. A total of 33 compounds have also been screened for anti-HIV activity. It has been observed that the compounds tested may be selectively toxic to HIV-infected cells, while not altering the viability of the non-infected cells. Additionally, three compounds were found to limit the activity of viral enzymes vital to the HIV life-cycle, and these will be further evaluated in Mintek’s in-house HIV screening and research Laboratory.

A biomedical screening laboratory will be fully commissioned by mid 2006, and will see the introduction of in-house chemotherapeutic testing at Mintek. This laboratory has been equipped as a Biosafety Level II (BSL-2) facility to allow for the investigation of infectious agents that are associated with human diseases. Immediate investigations will focus on HIV/AIDS, although research on malaria, TB, and cancer is also envisaged in the future. A wide range of novel gold compounds, synthesised by members of the AuTEK biomedical consortium, will be screened for potential activity against HIV. Compounds exhibiting inhibitory action towards the virus will be further developed and evaluated through extensive pre-clinical tests.

Project AuTEK received two NRF/THRIP awards in 2005. The first award was made for R&D that adds value to South Africa’s natural resources. The second, for the development of quality human resources for industry, was presented to Robert Tshikhudo for his PhD work in the AuTEK biomedical programme at the University of Liverpool.

Platinum group metalsProcess development work for new PGM projects continued at a high level of activity. Pilot milling and flotation work was undertaken on a 60 t sample of ore for the Blue Ridge project. Ridge Mining announced the development of this project in November 2005, and construction will start in the second half of 2006, with the first production scheduled for early 2008. A mini plant campaign was run for Ivanhoe Platinum to confirm that the target grades and recoveries could be achieved, and to generate concentrate for downstream testwork. Laboratory-scale work was carried out to define the flowsheets for Sheba’s Ridge (Ridge Mining) and Tuschenkomst (Platmin), and piloting on both these projects is planned for 2006. Small-scale testwork was also done for African

Platinum (Leeuwkop project), Anooraq Resources (Boikgantsho joint venture), Platinum Australia (Smokey Hills and Kalplats deposits), and Impala Platinum’s Shaft 17 expansion. Reagent testwork and cleaner flowsheet optimisation was undertaken for Impala’s Mimosa platinum mine.

Many new PGM projects involve multiple orebodies and more complex mineralogical characteristics, which require in-depth study. Several potential new milling procedures for PGMs have been identified, including densifiers, HPGR technology, and screening or attritioning technologies. The introduction of ultra-fine grinding into milling circuits in the future is a distinct possibility.

A major review was conducted on the application of recent developments in fine screening technology to the closed-circuit milling of UG2 ores. A techno-economic study indicated that the energy requirements for grinding could be reduced by more than 20 per cent, and that significant improvements in PGM recoveries could be expected. This work will continue during 2006.

The demand for certified PGM reference materials has grown significantly over the past two years, due to the number of new projects being evaluated and more stringent standards for geological resource evaluation and metallurgical accounting. Three new PGM reference materials are currently being manufactured from feed-grade UG2, Merensky, and Platreef, and the round-robin analyses and statistical evaluation will be completed by mid-2006. Ferrochromium metal and slag materials are also in production.

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Flotation testwork.

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Technical Review

Development of the Xanthoprobe, an instrument for the online measurement of free xanthate concentration in flotation cells, is at the prototyping stage, and plant trials are expected to begin by the fourth quarter of 2006. The instrument will form the basis of a control strategy, implemented on the StarCS control platform, to optimse xanthate additions so that the levels are sufficient for effective recovery but wasteful overdosing is avoided. The same principle is used very successfully to control cyanide additions on gold plants using the Cynoprobe.

Work on the AMIRA Project 671 was completed. This project, which was sponsored by Anglo Platinum, Impala Platinum, and Rio Tinto, involved a study of the behaviour of trace elements during matte smelting and an evaluation of methods for the analysis of trace elements in various streams generated during smelting. Sustainable operation of base metal smelters requires detailed knowledge of trace-element behaviour, and since the original project did not fully resolve these issues, a draft proposal for further work has been prepared for AMIRA.

A THRIP project has been launched, with support from Anglo Platinum, Impala Platinum and Lonmin Platinum, to study the containment of slag and matte in the furnaces used for matte smelting and in converting. Individual investigations focus on the corrosion of copper by sulphur and sulphur dioxide, gas-refractory interactions, and matte liquidus temperatures. Three MSc students are being trained at Mintek as part of the project. The project provides a forum for the PGM producers to undertake generic furnace-related studies, and enables Mintek to maintain close contact with industry.

The smelting step of Mintek’s proposed ConRoast process for the recovery of PGMs from high-chromium low-sulphur concentrates and other materials has been conclusively demonstrated in a long-term smelting campaign. By the end of financial 2005, almost 15 000 t of revert tailings and other materials had been processed in the DC arc furnace at feed rates of up to 35 t/day. The PGMs and base metals were recovered into an iron-based alloy that was returned to the smelter. The project showed that the alloy smelting process is efficient (the PGMs were upgraded by more than ten-fold, with more than 99 per cent of the Cr2O3 being rejected in the slag) as well as robust enough for industrial application. Small-scale converting tests in a top-bown rotary converter have shown that the alloy can be blown to a composition close to that of existing converter mattes.

The full ConRoast process involves the DC smelting of dead-roasted sulphide concentrates, with recovery of the PGMs and base metals from the alloy by leaching. ConRoast offers advantages in terms of being able to contain SO2 emissions (by removing essentially all of the sulphur in a continuous enclosed roaster upfront of the smelting), and to accommodate a much wider variety of feed compositions, with no constraint on the minimum quantity of base metal sulphides. Mintek has begun negotiations with a potential partner on a development programme aimed at leading to commercialisation of the process.

In 2004 Mintek was asked, through the Platinum Research Venture, to propose a programme to address issues concerning the industry’s compliance with statutory requirements for sulphur emissions.

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An integrated pilot plant for milling/

flotation flowsheet development.

Crushing a PGM ore sample for a new reference material.

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Technical Review

The first phase of the study, which involved collaborative trials conducted internationally between analytical laboratories to determine the precision and accuracy of sulphur measurements in various smelter streams, has been completed. This is being followed by an investigation of the sulphur balances around an industrial smelter operation.

The Platinum Development Initiative (PDI) is a collaborative programme to develop platinum-based analogues of the nickel-based superalloys used in turbine components. During the year under review, the anomalies identified in the binary phase diagrams which constitute the platinum-chromium-ruthenium system were largely resolved, and the ThermoCalcTM work will be completed in the second half of 2006. Castability tests of the experimental alloys yielded positive results, although further optimisation of the alloy composition will be needed. Discussions were held with the National Institute for Materials Science (NIMS) in Japan regarding the route to possible commercialisation of the current alloy in coatings for the turbine industry. The PDI is supported by Anglo Platinum, Impala Platinum, and Lonmin Platinum, with collaborating institutions NIMS and the universities of Bayreuth, Jena, and Leeds.

The Innovation Fund project on platinum-based jewellery alloys at the University of Cape Town was completed, with successful development of several hardenable ternary alloy compositions.

The Department of Science and Technology (DST) has granted additional funding for fast-tracking the commercialisation of platinum-based alloys in applications not covered by the PDI, including the glass industry, coatings, and powder metallurgy. The National Research Foundation’s Centre of Excellence for Strong Materials also granted funds for the purchase of high-temperature fatigue testing equipment.

Ferrous metalsConfirmatory testwork was done to assist in flowsheet design for Oriel Resources’ Voskhod chromite project in Kazakhstan. A scoping study, managed by SRK and with DRA consulting on the process and plant design, was completed in July 2005. However, the metallurgical input was based on previous technical reports and typical industry practice, since no suitable representative ore sample was available at that time. The subsequent testwork, which included comminution (Bond rod work index, crushability work index, and abrasion tests), gravity separation, and mineralogical studies, showed that the desired product grades for lumpy, chip and fine material could be readily attained using gravity methods. TCLP tests were carried out on the tailings, and the results were within the US Environmental Protection Agency’s specifications.

A major collaborative project has begun to develop a more cost-effective type of grinding ball for the minerals industry. The project, with a budget of R5 million spread over three years, is funded by the DST’s Innovation Fund, which is currently managed by the NRF. The project partners with Mintek are Anglo Platinum, the University of Pretoria, and Prima Industrial Holdings.

Five alloy compositions have been selected for initial investigations. Samples produced in laboratory-scale melts will undergo screening for their mechanical and metallurgical characteristics, and their microstructures will be optimised for the best combination of impact and wear resistance. Balls cast from the three most promising materials will then be evaluated through Mintek’s own quality control system. In the subsequent stages of development, batch tests, and finally full-charge performance trials, will be undertaken on industrial milling circuits. If a

page 17

Tapping molten PGM-enriched

alloy from the DC arc

furnace during demonstration of the smelting step in the ConRoast

process.

Quality control work on grinding balls in the metallographic laboratory.

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Technical Review

ball can be developed that exceeds the performance of current products at a more competitive price, it would result in a significant reduction in processing costs.

The planned trials of the “smart” rockbolt, or SmartboltTM, were completed at a local gold mine. After a review of the data from all the tests in conjunction with SIMRAC, which funded the development of the bolt, it was decided to conduct further trials in the high-stress areas of the mine. The trials are being funded by the Innovation Fund through the University of Kwazulu-Natal. A second mine, which is currently deepening its sub-shaft to below 3 300 m, has also expressed interest in having the bolts installed in critical areas. The Smartbolt, which makes use of a phase transition to warn of impending unstable rock conditions in underground mines, won a SABS 2005 Prototype Award.

Development and prototyping work on the low-nickel austenitic stainless steel for structural applications has been completed. Mintek has identified two potential local partners – one a manufacturer of bolts and the other of roof fasteners – with which to commercialise the alloy, and during 2006 batches of stock material will be supplied to them for the manufacture of test samples for clients.

Extensive characterisation testwork was done on 400 samples of manganese material for CVRD’s new project in Gabon. Characterisation is aimed at evaluating the manganese grade of samples at each size fraction, afterwards using gravity separation to upgrade the material to the target grade.

Testwork was initiated on the recovery of vanadium from and the upgrading of slag obtained from the smelting of the vanadium-bearing titanomagnetite layers that occur in the Upper Zone

of the Bushveld Complex. These layers constitute a significant resource of iron, titanium, and vanadium but technology for the recovery of all three valuable metals has yet to be developed.

A research project, which was begun in 2002 to investigate the mineralogical and geochemical nature of manganese ore alteration in the northern part of the Kalahari Manganese Field (KMF), neared completion. Results from the study will enable geologists working in the KMF to identify areas for selective mining that would benefit downstream beneficiation. Predictions based on the data obtained will guide exploration initiatives in the search for ore of optimum feed quality in metallurgical beneficiation for the ferro-alloy industry, as well as possible parameters to beneficiate the ore itself.

A large amount of service work was performed for Kumba Resources using the mineral density separator in support of the Sishen expansion project.

Non-ferrous metalsMintek is co-ordinator of the bioleaching work package in the European Union’s BioMinE project, which is part of the EU’s Sixth Framework Programme (FP6). Mintek’s major role is to create synergies between various R&D partners that are studying topics that are relevant in both southern African and in Europe. These include technologies for refractory gold deposits, complex polymetallic base metal deposits, and mining and metallurgical waste materials. Particular emphasis is placed on innovative research towards making these processes more sustainable from both the environmental and the economic point of view.

In collaboration with the university members of BioMinE, Mintek is also investigating the more fundamental application of modern biological techniques, such as biomolecular techniques

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The Smartbolt is interrogated with a portable ultrasonic USM 25 DAC device, which measures the longitudinal sound velocity to assess any

stress-induced microstructural

changes that have occurred in

the bolt.

The first copper cathode produced downstream of the bioheap-leach pilot plant at Sarcheshmeh, Iran.

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Technical Review

for identifying microbial strains and monitoring bioleaching processes, and the effect of changes in parameters such as pH, temperature, and metal concentration on the dynamics of microbial populations.

In addition to the EU FP6 funding, Mintek’s contribution to BioMinE is being supported by a major strategic investment by the DST.

Large-scale piloting of Mintek’s heap bioleaching technology for chalcopyrite-bearing copper ores is under way at the Sarcheshmeh Copper Complex in southern Iran. Irrigation of the first 25 kt heap was started in December 2005, with the first metal recovery by solvent extraction and electrowinning at the end of January. The throughput of copper in solution is expected to peak at about 300 kg/day, although this figure will vary according to the stage of the leaching process. A second heap will be started in mid-2006, followed by a third in the last quarter. Each heap contains about 90 t of extractable copper, and will take about 350 days to leach completely. The programme, which is being run under a collaborative agreement with the National Iranian Copper Industries Company (NICICO), is aimed at proving the technology at a large scale, and generating reliable operating information for a commercial-scale operation.

Mintek, in association with an industry partner and funded by the Biotechnology Partnership and Development (BioPAD), completed development of a cost-effective tank bioleaching technology for zinc sulphide concentrates. The novel process, which results in the oxidation of sulphide to elemental sulphur rather than complete oxidation to sulphate, is tailored as a cost-effective roaster debottlenecking tool. Operating in parallel with a roaster, the bioleach process should handle sphalerite feedstocks containing contaminants such as iron and arsenic more effectively than can currently be done by roasting. Mintek will seek to implement this technology in industry, both in southern Africa as well as in Europe through opportunities that may arise through its participation in BioMinE.

A second BioPAD-funded project involves the development of a novel and effective technique for inoculating bacteria into leach heaps. Laboratory-scale work has demonstrated the production of high concentrations of bacteria in a novel growth reactor and the alteration of their adhesive characteristics using appropriate storage conditions. Small-scale column leach tests carried out to simulate the inoculation process have shown that as well as a more rapid start-up, an enhanced rate of pyrite oxidation can be obtained, which will lead to higher heap temperatures and faster copper leaching

kinetics. Mintek is now looking for a potential end-user willing to participate in large-scale piloting testwork at a mine site.

Two MSc projects supported by Mintek were started in 2006, one on the bio-transformation of laterites and one on kimberlites. A MTech project is under way on the development of AFM techniques for studying bioleaching processes.

Laboratory testwork was conducted at Mopani Copper Mines’ Nkana Division in Zambia to purify the cobalt stream to obtain a solution suitable for cobalt metal production. The testwork, which consisted of copper and iron removal by ion exchange and solvent extraction for zinc removal and cobalt recovery and purification, was followed by an on-site pilot plant exercise that tested several different flowsheets. At the end of the year under review a second pilot-plant campaign, which included electrowinning of cobalt metal, was undertaken at Mintek with the participation of technical staff from Nkana to optimise the chosen flowsheet while running in a closed-circuit configuration.

A full flowsheet development exercise, encompassing milling of a 4 t bulk sample, composite sample preparation, leaching, and recovery of copper and cobalt by solvent extraction and electrowinning, was carried out for Africo Resources’ Kalukundi project in the DRC. Kalukundi, which is scheduled to start up in the first quarter of 2008, will have an annual production of about 16 400 t of copper and 3 800 t of cobalt.

A continuous mini-plant exercise, consisting of atmospheric and pressure leaching, various

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The Mintek-Bateman MeTRIX modular resin-in-pulp demonstration plant.

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Technical Review

stages of solution purification by precipitation, ion exchange and solvent extraction, and electrowinning of cobalt and copper, was carried out to develop a hydrometallurgical process for the Idaho Cobalt project (Formation Capital Corp). Further work to optimise the selected flowsheet is planned for 2006. The project, which is currently in the final feasibility and advanced permitting stage, will be the only primary cobalt mine in the western hemisphere, with an annual output of 1 500 t of cobalt metal and cobalt chemicals per year - equivalent to 3.3 per cent of the entire global cobalt supply.

On-site piloting using precipitation and solvent extraction was conducted at Impala’s Springs Refineries to purify the nickel and cobalt streams from the Ambatovy nickel deposit in Madagascar. Although the project was successful, Impala subsequently withdrew from the Ambatovy joint venture due to investment criteria, leaving Dynatec and Sumitomo Corporation as the sole stakeholders.

Under their collaborative agreement to develop and implement resin-in-pulp (RIP) technology for the metallurgical sector (Annual Report 2004), Mintek and Bateman commissioned a modular plant that will be used to demonstrate the potential of RIP technology for improving recoveries at various base-metal plants in southern and central Africa. A particular application will be the re-treatment of residues and waste streams – for which RIP is particularly suited, since it is effective on low-grade streams (less than 5 g/l), and in the case of re-pulped residues, it lessens or eliminates the costly solid/liquid separation step required in competing technologies. A further important benefit is a reduction in the environmental consequences of the waste. The skid-mounted plant consists of four adsorption stages and an elution circuit, and has a design throughput of 10 m3/h. A novel resin concentration meter is used to

monitor the resin concentration in each stage, and is linked to a PLC/Scada system that controls the resin inventory profile and the slurry and resin residence times.

Laboratory work was undertaken for the Kamoto joint venture on solution purification and cobalt solvent extraction, to verify plant performance and assess the option of incorporating solvent extraction to purify the cobalt electrolyte prior to electrowinning. The joint venture is rehabilitating the Kamoto underground mine, concentrator, and Luilu metallurgical plant in the DRC with a view to restoring historical levels of production.

Preliminary bench-scale testwork was carried out on the carbochlorination of zirconium in a bubbling fluidised-bed reactor to produce zirconium tetrachloride, which is an intermediate in the production of zirconium metal and chemicals. However, it was found that the reaction is extremely slow, and consequently the process would not be economically viable.

A study was made into the feasibility of establishing a national fluidised-bed facility in South Africa. Fluidised-bed reactors can process fine, low-grade materials, and offer better energy efficiencies and lower emissions compared with competing processes. However, the companies that displayed interest in the project saw the benefits of fluidised-bed technology in terms of contributing to their energy requirements, for example through the combustion of low-grade coals, biomass, and waste materials, rather than meeting their process needs. In general, the metallurgical industry saw little need for such a facility, since there appears to be no lack of suitable resources to run existing processes.

A further demonstration campaign was run over

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Electrowinning of cobalt metal during testwork

for Mopani Copper Mines.

Overview of the bioheap-leach operation at Sarcheshmeh, showing the pregnant leach solution ponds (blue) and the raffinate pond (green due to the presence of ferric ions), with the ponds for the second heap beyond.

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Technical Review

a period of eight days on Mintek’s novel zinc refining process, which is based on a DC-furnace boiler and a packed-bed distillation column. At steady state, the refined zinc production was 30 kg/h, and the product metal was within specifications for Special High Grade (less than 30 ppm lead, germanium, manganese, and copper). This provides an important step in a possible method of recovering germanium and zinc from slag dumps arising from lead smelters.

An Innovation Fund project on the evaluation of new technologies for the production of titanium metal was continued in 2005/06. The consortium partners working with Mintek on the project are the CSIR, the University of Pretoria, and Risimati Engineers. An initial technology scan was followed by a more detailed techno-economic evaluation of short-listed processes and a market study of titanium metal.

Another Innovation Fund project has succeeded in developing a less expensive method of producing aluminium-titanium master alloy, using titanium dioxide (TiO2) as the starting material rather than titanium metal. A more potent Al-Ti-C grain refiner, with a better refining capability than currently available commercial products, can also be produced using Mintek’s patented process of aluminotherimic reduction of TiO2. The production technology for the aluminium-titanium alloy is being commercialised in conjunction with Zimalco.

Following the successful conclusion of R&D on the technical aspects of the Mintek Thermal Magnesium Process (Annual Report 2005), Mintek and Anglo American reviewed the economics of the process and agreed in principle on a programme of work to take the technology forward. Small-scale testwork has confirmed that the product metal can be refined to commercial purity, and a feasibility study for a demonstration-scale magnesium smelting facility is scheduled for completion by the end of 2006. A possible outcome of this work could be the eventual establishment of a magnesium metal production facility in South Africa, which would support the local automotive sector and complement the region’s fast-growing aluminium industry.

Industrial mineralsMineral separation testwork using a 50 t/h X-ray transmission sorter was carried out. The machine, which sorts material in the size range between –80 mm and +10 mm, discriminates between particles on the basis of their atomic number. Successful results were obtained on a coal sample, and this work will be extended to other mineral separations in the forthcoming year.

A laboratory facility has been set up to characterise the physical properties of diamonds.

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Constructing the pulsed columns for uranium extraction at the Olympic Dam project, Australia. Pulsed-column technology has been chosen for the solvent extraction circuit at the Dominion uranium project in South Africa (Photo courtesy Bateman).

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Technical Review

The first two commercial projects for the diamond characterisation facility commenced towards the end of the 2005/06 financial year. In addition, the electron microscopy section has refined its methods for analysing diamond indicator minerals, and analyses were provided for several national and international clients on a commercial basis. The first of several commercial projects on bauxite ores commenced towards the end of the 2005/06 financial year. HLS testwork for De Beers was done on an ongoing basis to verify plant efficiency.

An investigation on the Marropino tantalum deposit in Mozambique was undertaken to design a suitable scrubber for the plant. The results from the project were used by Bateman to design and build a scrubber that will be installed on the plant.

Mintek was very active in uranium process development until the early 1980s. Although there was limited demand for uranium R&D in the ensuing years, Mintek maintained its expertise in uranium extraction, which has made re-entry into this field relatively easy.

Further laboratory-scale testwork was undertaken to optimise the flowsheet for Paladin Resources’ Langer Heinrich project in Namibia. Process development work on this project, to provide input to the bankable feasibility study by GRD Minproc, was completed during the previous year. The alkaline nature of the ore requires a carbonate/bicarbonate leach, and the clarified leach liquor will be subjected to ion exchange to upgrade the uranium concentration and purity, followed by yellowcake precipitation from the eluate. Mintek is also assisting GRD Minproc with metallurgical testwork to establish a flowsheet for Paladin’s Kayelekera project in Malawi. The project is still at an early stage of development.

The Dominion project of SXR Uranium One will use pressure leaching to obtain the required high recoveries. The clarified leach liquor will be upgraded by solvent extraction, and ammonium diuranate precipitated from the strip liquor. Pilot plant testwork at Mintek has resulted in Bateman Pulsed Column (BPC) technology, as used at Olympic Dam in Australia, being chosen for the solvent extraction step. This will be a first in Africa. Additional stripping tests using the BPC with pH control gave very encouraging results (currently at Olympic Dam only extraction is performed in the BPC). Bateman conducted the feasibility study on this project.

In addition, testwork was undertaken to obtain design criteria for a new elution system at

AngloGold Ashanti’s Vaal River Uranium Plant. The ion exchange resin is prone to silica fouling, a well-known phenomenon that decreases both the loading capacity of the resin and its stripping efficiency, leading to lower recoveries. It was shown that the resin could be regenerated with sodium hydroxide to remove more than 90 per cent of the silica, largely restoring its performance.

Mintek has undertaken mineralogical investigations on a variety of ores from both primary and secondary uranium deposits. Quantitative scanning electron microscope techniques such as MLA and QEMSCAN are used to determine liberation characteristics, particle size distributions and mineral abundances. In particular, a knowledge of the mode of occurrence of unrecovered uranium in tailings and residues should enable upgrading procedures to be improved.

Uranium ores produced in southern African until now have been processed using relatively mild acid leaching conditions followed by ion exchange and/or solvent extraction from simple liquors. However,

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NIMCIX ion exchange columns at the Vaal River uranium plant (photo courtesy AngloGold Ashanti Ltd.).

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Technical Review

many new projects are likely to require more complex technologies. The Karoo sedimentary uranium ores contain calcite and sulphide minerals and are thus both acid- and base-consuming, so the choice of lixiviant would be based on economic grounds. Technical challenges appear to include efficient liquid/solid separation, and the effective handling or recovery of molybdenum. Low-grade calcrete deposits might require heap leaching and recovery of both uranium and vanadium, whereas for a relatively high-grade material, where the uranium appears to be present in the refractory mineral davidite, the challenge would be to achieve adequate leaching efficiency. Ores that are difficult to settle or filter could be amenable to RIP.

Pyritic ores are ideally suited to bioleaching, since the pyrite provide a substrate for bacterial growth and produces the ferric sulphate and sulphuric acid necessary for uranium oxide leaching. The use of thermophilic micro-organisms for uranium leaching can now be considered, and is likely to lead to considerably faster kinetics, resulting in lower processing volumes.

Quality, environment and safetyMintek successfully underwent an assessment audit for ISO 9001 in August 2005. The next assessment audit, for ISO 14000, is due to be carried out in August 2006, and that for OHSAS 18001 the

following year. Assessment audits are performed on a three-yearly basis for certification renewals.

Mintek’s Analytical Services laboratories underwent a successful surveillance audit for ISO 17025 compliance in early 2005. The next audit is due towards the end of 2006.

At the end of the period under review, the Lost Time Injury Frequency Rate (LTIFR) was 1.7, compared with the target of 1.0. The new Client Dissatisfaction Frequency Rate (CDFR) target of less than 10 was achieved at the beginning of 2006, with improved delivery times being identified as a major contributing factor to the decrease. The CDFR is measured by conducting client feedback surveys for all completed projects costing more than R20 000.

During 2006, two new targets will be established: for Public Dissatisfaction Frequency Rate (complaints from the general public) and for Major Environmental Impacts.

Owing to the increase in uranium-related R&D, Mintek has appointed a Radiation Protection Specialist (RPS), who is registered with the National Nuclear Regulator (NNR). A Radiation Protection Programme (RPP) has been incorporated as part of the overall Quality Management Programme, and an internal audit schedule, which incorporates a site inspection programme, has been implemented to ensure that the RPP remains relevant and is updated as approved by the NNR. Mintek is registered as a uranium testwork facility with the NNR and the Department of Minerals and Energy (DME).

In terms of South Africa’s national Energy Efficiency Strategy, Mintek has undertaken to meet an energy saving target of 1.2 per cent each year between 2006 and 2010. Monitoring equipment will be installed at various points around the site, and this will enable Mintek to ascertain the energy requirements of various operations and identify where consumption could be reduced.

Small-scale testwork has confirmed that the product metal can be refined to commercial purity, and a feasibility study for a demonstration-scale magnesium smelting facility is scheduled for completion by the end of 2006.

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Mintek’s Radiation

Protection Officer checks the

radioactivity of a bulk sample

arriving at Mintek for pilot plant

work.