Chitosan sorbents for platinum sorption from dilute solutions

Chitosan has proved efficient at removing platinum in dilute effluents. The maximum uptake capacity reaches 300 mg g(-1) (almost 1.5 mmol g(-1)). The optimum pH for sorption is pH 2. A glutaraldehyde cross-linking pretreatmen t is necessary to stabilize the biopolymer in acidic solutions. Sorption is otherms have been studied as a function of pH, sorbent particle size, and t he cross-linking ratio. Surprisingly, the extent of the cross-linking (dete rmined by the concentration of the cross-linking agent in the treatment bat h) has no significant influence on uptake capacity. Competitor anions such as chloride or nitrate induce a large decrease in the sorption efficiency. Sorption kinetics show also that uptake rate is not significantly changed b y increasing either the cross-linking ratio or the particle size of the sor bent. Mass transfer rates are significantly affected by the initial platinu m concentration and by the conditioning of the biopolymer. Gel-bead conditi oning appears to reduce the sorption rate. While for molybdate and vanadate ions, mass transfer was governed by intraparticle mass transfer, for plati num, both external and intraparticle diffusion control the uptake rate. In contrast with the former ions, platinum does not form polynuclear hydrolyze d species, which are responsible for steric hindrance of diffusion into the polymer network.