Studies On Biodegradation Of Organic Flotation Collectors Using Bacillus polymyxa

Abstract

Numerous organic reagents of diverse structural composition are employed in the froth flotation process for the beneficiation of non-metallic and sulphide ores. Alkyl xanthates are used as collectors for sulphide ores while amines and fatty acids are used for non-metallic ore beneficiation. Although these collector reagents react preferentially with the concerned minerals in the treated ore pulp, excess and unreacted concentration of these organic collectors end up in the mill process effluents. It has been known that even small concentrations of these organic reagents in water streams are toxic to water life, besides their deleterious influence on end stream processes during recycling. Bioremediation has long been recognised as an inexpensive, flexible and environmentally benign technique for waste water treatment. These organic flotation reagents are amenable to biological degradation.

The major objective of this work is the degradation of solubilized collector reagents from aqueous solutions using a microbial technique. Bacillus polymyxa, a Gram-positive, neutrophilic, periflagellated heterotroph that occurs indigenously in soils and certain mineral deposits has been used in the bioremediation studies. Organic flotation reagents namely, dodecyl ammonium acetate (DAA), which is used as a collector for oxides and silicates, sodium isopropylxanthate which finds application in sulphide flotation and sodium oleate, mainly used for oxide and salt-type minerals, have been chosen for the degradation studies. Pure minerals of galena, pyrite, magnetite, quartz and calcite have been typically selected for these investigations.

The growth of Bacillus polymyxa in the presence of these organic reagents at different concentrations has been assessed and the degradation of these reagents monitored. Attempts have been made to grow the bacterium in the presence of the organic reagents, both in the absence and presence of sucrose, by adaptation technique. Electrokinetic studies on the chosen minerals namely, galena, pyrite, quartz, calcite and magnetite have been carried out both in the presence of the organic reagents and Bacillus polymyxa cells or metabolite. Biological stripping of the adsorbed collector reagents from the mineral surfaces have been examined through FTIR spectroscopy. The progress of bioremoval of the organic reagents along with the generation of newer reaction products has also been monitored through uv-visible spectroscopic technique.

The results of this study highlight that Bacillus polymyxa and its metabolic products bring about the degradation of the chosen organic flotation collectors. Further, the bacteria are able to utilise the collector reagents as carbon source for their growth, in the absence of added organic carbon (sucrose). Electrokinetic studies and examination by FTIR spectroscopy reveal that consequent to interaction with Bacillus polymyxa, significant surface modification on the mineral takes place. Probable mechanisms in the biodegradation processes are illustrated. Biological metabolic products responsible for bringing about the bio-deterioration have been analysed and characterised.