Biosorption of arsenic (V) with acid-washed crab shells.

Highly toxic arsenate occurs naturally in some well water as well as in industrial wastewaters. Removal of arsenate (As(V)) by biosorption with acid-washed crab shells (AWCS) is very sensitive to solution pH. It greatly increased when the solution pH was lowered from 3.44+/-0.07 to 2.51+/-0.02, but it was reduced at pH below 1.99+/-0.01. Change of solution pH not only affected the charged functional groups on AWCS but also the speciation of arsenate in solution. Increasing ionic strength of solution negatively affected the arsenic uptake. At ionic strength 0.1M, arsenic uptake was seriously depressed. Arsenic biosorption with AWCS was mainly through arsenate binding on the amide groups in the AWCS. AWCS has a dense structure and low extent of swelling in aqueous solutions. This might prevent effective arsenate access to the functional groups in AWCS.