Abstract
M.Sc.
Inorganic pollutants like heavy metals are some of the major water pollutants
worldwide. They are toxic and in some cases carcinogenic even at low
concentrations. Their removal from industrial aqueous solutions, wastewater and
hydrometallurgical process solutions prior to their release to the environment is
necessary for a healthy biosphere which includes human beings, aquatic life and
plants.
There are several technologies used to remove metals such as Cu, Co, Zn, Hg
from water. These include among others, ion exchange, membrane filtration,
activated carbon, electrochemical treatment, chemical precipitation, reverse
osmosis, coagulation and flocculation. Although they have been used in the
removal of metal pollutants from water, these technologies produce high quantities
of sludge. They are also expensive to operate and need well trained personnel to
operate large chemical plants. Since current metal removal techniques have
limitations, a need exists for the development of environmentally friendly and cost
effective techniques for the removal of metal ions from aqueous media.
The focus of this research project is on the use of micro-organisms as biosorbents
for copper and cobalt pollutants in aqueous solutions. The experimental work was
carried out on a laboratory scale and a summary of our findings is presented as
follows:
Synthetic sulphate solutions of copper and cobalt were prepared using
CuSO4. 7H2O and CoSO4. 5H2O powders. Concentrations of 0.002 M,
0.07 M and 0.2 M copper and cobalt ions in solution were used as test
synthetic solutions for our experiments.
Mixed strains of bioleaching bacteria were sourced from Mintek (Randburg,
South Africa) to test the viability of this research project. This consortium
contained Acidithiobacillus caldus, Leptospirillum spp, Ferroplasma spp and
Sulphobacillus spp. These bacteria were able to remove up to 55% copper
and 25% cobalt from low concentrated copper and cobalt sulphate solutions
with 69% and 58% removal demonstrated in the case of mine effluents
emanating from metallurgical operations.
Different strains of micro-organisms (bacteria) were isolated from mine
dumps and mine operation effluents and soil from the Palabora Mining
Company in Limpopo, a northern province in South Africa and Nigel Town
in the Gauteng Province.
The isolated bacterial strains were then identified using PCR analysis and
strains from the Bacillus genre were found to be predominant. Shewanella
spp was also present. Pseudomonas spp was isolated using Pseudomonas
agar base.
These bacteria were then cultured at different species-specific culture
conditions and their capabilities to remove copper and cobalt ions first from
synthetic solutions and subsequently from mine effluents emanating from
metallurgical operations were tested. In the first stage of biosorption
experiments, factors that affect biosorption mechanisms which include,
solution concentration, biomass concentration, pH, contact time and the
presence of other metal co-ions were investigated.
A decrease in the amount of metal sorbed as solution concentrations
increased was observed with all the bacterial strains. An increase in metal
sorption was also observed when biomass concentration was increased.
The pH was found to be a species dependant parameter.