BIOSORPTION OF TRACE ELEMENTS FROM AQUEOUS SYSTEMS IN GOLD MINING SITES BY THE FILAMENTOUS GREEN

ALGAE (Oedogonium sp.)

E.N. Bakatula1, E.M. Cukrowska1, I.M. Weiersbye2 & H. Tutu1

1School of Chemistry, 2School of Animal, Plant and Environmental Sciences University of the Witwatersrand, Johannesburg

July 2013

IntroductionObjectivesExperimental workResults and discussionConclusion

Presentation outline

They must be removed from the polluted streams in order to meet increasingly stringent environmental quality standards.

Heavy metalsSpecial concern

Non-biodegradable

Toxicity

BioaccumulationPersistent

Budget up as travelling food chain – serious threat to humans and animals

The entire environment is at stake

Introduction

Effluents generated by the mining activities in South Africa result in several environmental challenges, among which water pollution has been the most significant.

They contain large quantities of toxic substances, such as cyanides and heavy metals, which have serious implications on human health and ecologically.

Several methods have been proposed to remediate mine wastewaters but most of them are either inefficient or very expensive and also have drawbacks.

Physico-chemical remediation

Phytoremediation = Green remediation

Coagulation – flocculation Reverse osmosis; Flotation Ultra-filtration; Ion exchange; Precipitation ; Electro-dialysis Activated carbon adsorption

Use of plants to partially or substantially remediate selected substances in contaminated soil, sludge, sediment, groundwater, surface water and wastewater. (Pivetz, 2001).

Introduction cont....

Micro-organisms are stimulated to degrade hazardous organic and inorganic contaminants to environmentally safe levels in soils, subsurface materials, water, sludge, and residues.

Bioremediation

Biosorptive properties of green algae: Oedogonium sp.

Oedogonium is an unbranched, filamentous green algae with distinctive rings at the apical ends of certain cells.

Biosorption in algae has mainly been attributed to the cell wall properties where both electrostatic attraction and complexation can play a role. The cell wall consists of:- polysaccharides – cellulose, fucoidan, fucose, alginic acids or alginate.........

Alginic acid

-proteins (chitin) and phosphate carbohydrates and hence offers a number of active sites capable to bind metal ions, they may act individually or in synergy.Biosorption is a passive metabolic process, reversible and occurs at a faster rate.

The complex structure of the algae implies many ways for the metal to be taken up. The biosorption mechanisms are various and not fully understood.They may be classified according to various criteria;depending on the location.

Mechanism of the biosorption

Advantages of the biosorption

Low cost High efficiency

Minimisation of chemical and biological sludge Ecofriendly nature

Used both in situ and ex-situ High efficiency in dilute effluents

Regeneration of biosorbent Possibility of metal recovery

Objectives

This research investigated the potential use of the filamentous green algae (Oedogonium sp.) for the removal of Cu, Co, Cr, Fe, Hg, Ni, Zn and U in multi-ion system from mines wastewater.

To assess the effects of contact time, pH, concentration and temperature on the adsorption capacity.

To investigate the regeneration of such materials for a potential re-use and recovery of some valuable metals.

EXPERIMENTAL WORK

The algal strains were collected from a dam wastewater bodies receiving gold mining effluent.

Metal analysis of the dam water as well as the metal concentration at equilibrium was done using the ICP-OES.

3. Batch adsorption studies of Cu, Co, Cr, Hg, Fe, Ni, Zn and U in multi-ion system onto algal biomass

a. Effect of pH (2 – 7) b. Effect of initial metal concentration (50 - 500 mg/L) – Adsorption

isothermsc. Effect of contact time (10 – 180 min) – Kinetic studyd. Effect of temperature (20 and 40oC) – Thermodynamic parameters

4. Desorption of metals adsorbed ( 0.1 M HCl) and re-use of the biomass

2. Characterisation of the algal biomass- FT-IR- CHNS

1. Preparation of algal biomass - Washing with D-H2O

Freeze dried

RESULTS AND DISCUSSION

1. Characteristic of the biomass

Elemental composition (CHNS)

C:24.9% N: 4.12% S: 5.85%

FT-IR Spectra

OH; NH

COOH; NH; CO; PO4

-3

C-C; -CN

OH

CH

• The algal sample had functional groups, namely: carboxylic acids, amines, alkanes, alcohols, ethers.• The class of compounds present in the algae are therefore: carbohydrates, organic acids, proteins, polysaccharides.....

Water bodies from the dam was polluted with the following:

Results and discussion, cont.....

2. Metals analysis

EC – 2.372 mЅ.cm-1

pH – 8.57Metal mg/L Metal mg/L Metal mg/L

Ag 0.075 Co 1.6 Mg 38

Al 3 Cr 0.2 Mn 196

As 0.04 Cu 0.15 Ni 1.25

Au 0.98 Fe 22.5 Zn 2.5

Pb 0.07 U 0.045    

The results point to pollution of the dam by toxic elements, with concentrations higher than the regulated limit by the Department of Water Affairs (SAWQ, 1996).

Co 0-50 μg/L; Cr 0-20 μg/L; Cu 0-200 μg/L; Ni 0-200 μg/L; Zn 0-1000 μg/L; U 0-0.4 μg/L

Fe 0-500 μg/L (SAWQ).

2 3 4 5 6 7 8

35

40

45

50

55 Cu

Ni

Zn

Co

pH

qe

(mg

g-1

)

2 3 4 5 6 7 8

35

40

45

50

55FeHgUCr

pH

qe

(mg

g-1

)

Effect of pH on the biosorption of Cu, Co, Cr, Fe, Hg, Ni, Zn and U for Oedogonium sp. in a multi-component solution (Ci = 100 mg L-1, pH = 3, algal mass = 1g, Temp = 25 oC)

Uranium species in aqueous solution

3. Adsorption studiesEffect of pH

Parameters of the Langmuir, Freundlich and D-R models for the adsorption of metals onto oedogonium sp. biomass in multi–ion system

Effect of initial metal concentration – Biosorption isotherms

The adsorption of Cu, Co, Cr, Hg, Ni and Zn fitted the freundlich as well as the D-R isotherms – bound on heterogeneous surface with ion exchange being the main process.

Fe and U are not described by any of the cited models.

Metal Langmuir constant Freundlich constant Dubinin-Radushkevich constant

b(L/mg)

qm

(mg/kg)

R2 n KF

(mg/g)

R2 Xm (mol/kg)

Es(kJ/mol)

R2

Cu 56.72 0.409 0.909 3.866 1.133 0.965 1.014 10.62 0.961

Co 19.94 0.391 0.894 3.108 1.131 0.996 1.066 8.577 0.992

Cr 45.05 0.681 0.999 4.118 1.155 0.998 1.183 10.18 1.000

Fe 56.64 0.142 0.310 3.929 0.924 0.321 0.815 10.17 0.352

Hg 562.3 0.188 0.996 3.347 1.110 0.993 1.088 10.62 0.997

Ni 16.98 0.446 0.577 3.055 1.141 0.991 1.124 8.323 0.989

Zn 66.89 0.559 0.439 3.969 1.134 0.956 1.153 10.28 0.954

U 383.5 0.091 0.594 2.907 1.083 0.912 1.084 9.428 0.906

Effect of contact time – Kinetic study

Effect of contact time on the biosorption of Cu, Co, Cr, Fe, Hg, Ni, Zn and U for Oedogonium sp. in multi- component solutions (Ci = 100 mg L-1, pH = 3, algal mass = 25 g, Temp = 25oC)

The maximum adsorption was reached after 30 minutes.

The biosorption process followed the pseudo-second-order kinetic with R2 > 0.980 for all the metals studied.

0 50 100 150 200

0

10

20

30

40

50 Cu

Ni

Zn

Co

Time (min)

qe

(m

g/g

)

0

10

20

30

40

50

0 50 100 150 200

Time (min)

qe (m

g/g)

Fe

Hg

U

Cr

Kinetic Equilibrium

It appeared that the biosorption of Ni was controlled by the film diffusion process with the coefficient value of 10-7 cm2/s (Df = 0.23 r0 δ qe / t½ , according to Michelson, Df = 10-6 - 10-8 cm2/s).

The biosorption of metal-ions in a multi-ion system decreases with an increase in temperature. The process was spontaneous and exothermic.

Effect of temperature – Thermodynamic parameters

  qe ∆ H ∆ G  

 

mg g-1

kJ mol-1 kJ mol-1  293.15 K 313.15 K

293.15 K 313.15 K

Cu 46.7 44.9 -5.535 -2.38 -2.476

Ni 45.4 42.7 -8.634 -2.449 -2.598

Zn 47.2 47.2 -0.598 -2.364 -2.354

Co 46.6 46.4 -0.605 -2.396 -2.385

Fe 43.3 42.8 -1.635 -2.564 -2.593

Hg 49.93 49.41 -1.494 -2.243 -2.217

U 45.7 45.3 -1.238 -2.433 -2.454

Cr 46.3 45.2 -3.386 -2.401 -2.46

qe = amount adsorbed; ∆ H = Enthalpy change; ∆G = Gibb’s free energy

4. Regeneration and re-use of the algal biomass

0

20

40

60

80

100

120

Cu Ni Zn Co Fe Hg U Cr

So

rpti

on

%Adsorption Desorption

More than 110% of the metals adsorbed were eluted from the biomass. These results indicate that there were metals initially adsorbed on the biomass which were also released during desorption.

This virtually increases the adsorption efficiency of the Oedogonium sp. during the repeated adsorption-desorption operations.

Cycle: adsorption-desorption

0

10

20

30

40

50

60

Cu Ni Zn Co Fe Hg U Cr

Ad

sorp

tio

n c

apac

ity

(mg

/g)

Cycle 1 Cycle 2 Cycle 3

Conclusion and future work

• The algal biomass grows naturally in the vicinity of the tailings facilities and water systems, making it possible and cost-effective to be cultured in situ and for the clean up of the contaminated water.

• This research highlights the potential of algal biomass for use in metal bioremediation.

• The results indicate that Oedogonium sp. is an effective biosorbent for Cu, Co, Cr, Fe, Hg, Ni, Zn and U. The maximum adsorption capacity of untreated algal biomass was found to have comparable values to the ones reported in literature.

Assess the adsorption performance of the algal biomass on column mode and then use this biomass to monitor in situ the metals removal from polluted stream draining artisanal gold mining - to test the efficacity of biological filters.

Acknowledgements

• Dr H. Tutu• Prof E.Cukrowska• THRIP• Anglogold Ashanti• Wits University

THANK YOU !!!