Biosorption of chromate and vanadate species with waste crab shells

Waste crab shells from sea food industrial processing, containing chitin and protein, showed a promising potential for metal binding. A binary biosorption system of chromate and vanadate with Acid Washed Crab Shells (AWCS) was studied at pH 2.5 and 0.1 M NaCl. AWCS showed a higher affinity for vanadate than for chromate at the concentration ratio of vanadium to chromium from 0 to 1.5 in the solution. The presence of chromate did not affect the vanadate uptake within the concentration range examined. However, the chromium uptake was reduced down to 40% in the presence of vanadate. The results indicated that vanadate could be selectively separated from the vanadate–chromate mixture with the AWCS material. Based on the model parameters regressed from the respective mono-metal systems, the developed multi-component Langmuir model reasonably predicted the interference of vanadate on chromate uptake. In addition, the mono-vanadium Langmuir model very well predicted the vanadium uptake in the chromium and vanadium binary system.