Removal of Cr (III) and Ni (II) from tannery effluent using calcium carbonate coated bacterial magnetosomes

Abstract

Heavy metal contamination of surface water bodies and ground water has been a major problem around the world. Calcium-based adsorbents are effective but cannot be separated easily after the treatment. Magnetosomes are biogenic magnetite synthesised as highly ordered chain-like structures by magnetotactic bacteria. In this study, we have prepared magnetically controlled calcite microcrystals using magnetosomes for the adsorption experiment. The ability of magnetic calcite as adsorbent was investigated for the removal of Cr (III) and Ni (II) ions from synthetic solution. Critical parameters, such as the effect of pH, temperature, contact time, initial ion concentration, and adsorbent dose, were optimised in comparison with calcite, magnetosomes, and activated carbon for maximum metal ion removal. The study showed that equilibrium was established in 1 h for both Cr (III) and Ni (II) at a pH of 6.0 and 8.0, respectively. The adsorption process follows pseudo-second-order reaction kinetics, along with Langmuir and Freundlich adsorption isotherms. The thermodynamics of adsorption of both metal ions on magnetic calcite showed that the adsorption was spontaneous and endothermic in nature. Magnetically controlled calcite crystals successfully removed Cr (III) and Ni (II) from collected tannery effluent and separated from the solution by applying magnetic field. Maximum removal of chromium and nickel (94 and 84%) by magnetic calcite is similar to calcite crystals but higher than magnetosomes and activated carbon. The results indicated that magnetic calcite could be used as an alternative adsorbent for removing heavy metals from tannery effluent.

Industrial waste: Does it attract?

Bacterial magnetosomes coated with calcite can adsorb heavy metals from industrial waste while being easily recoverable with a magnet. The tanning industry produces large volumes of wastewater contaminated with heavy metals, and these toxins require removal prior to waste discharge into the environment. Calcium carbonate adsorbs heavy metals with high efficiency, but is difficult to recover from treated water, lowering water quality. A team led by Krish Suthindhiran at VIT University in India combine environmentally-innocent magnetosomes—magnetic iron-based minerals enveloped by lipid membranes and produced by magnetotactic bacteria—with a calcium carbonate coating to achieve materials that not only remove Cr(III) and Ni(II) from tannery effluents with efficiencies of up to 94% and 84%, but are easily separated post-treatment by application of a magnetic field.