Chitosan was examined as a means of removing soluble silver from industrial waste streams. Stirred-batch and column methods were used to remove free (hydrated) silver ion as well as the ammonia, thiocyanate, thiosulfate, and cyanide complexes of silver in simulated wastewater at an initial concentration of 50 ppm and in a pH range of 2-10. An actual sample of X-ray film development rinse water was also tested. Batch method results show 80-95% silver bound at pH 4-8 for Ag + and Ag(NH 3 ) 2 + , while 92% and 75% of Ag(S 2 O 3 ) 2 3and Ag(SCN) 3 2-, respectively, were bound at pH 2. Using a column containing 0.500 g of chitosan, 160 bed volumes of Ag + , 875 bed volumes of Ag(NH 3 ) 2 + , 715 bed volumes of Ag(S 2 O 3 ) 2 3-, and 190 bed volumes of Ag(SCN) 3 2solution were treated before silver ion concentration in the effluent reached 5 ppm. Chitosan did not significantly bind Ag(CN) 2at any pH tested. Chitosan treated 450 bed volumes of 40 ppm X-ray rinse water before effluent silver concentration reached 5 ppm. Capacity experiment results using the column method indicated 42 mg of silver bound per gram of chitosan. Four commercial resins, Amberlite IRA-67, IRA 458, IRC-718, and Duolite GT-73, were also tested as silver binding agents.

SY N 0 PSISSeveral new chitosan derivatives were synthesized with the intent of forming polymers that could be used in hazardous waste remediation as toxic metal-binding agents in aqueous environments. The ability of these derivatives to bind Cu2+, Pb2+, Cd2+, and Fez+ was tested and compared to chitosan. Four of the new compounds, the products of the reaction of chitosan with mercaptosuccinic acid, thiirane, pyridoxal hydrochloride, and succinamide, show promising results as binding agents for the above metal ions. The compound with mercaptosuccinic acid bound twice as much Cd2+, five times as much Pb2+, and virtually no Fez+ when compared to chitosan. The compound with thiirane bound three times as much Pb2+, whereas the pyridoxal hydrochloride derivative bound 30% more Cu2+ and twice the Pb2+. The succinamide derivative gave results comparable to chitosan, but with decreased solubility at low pH.

An optimum pH of 5.0 for the adsorption of Cr 6ϩ by chitosan was determined by using a stirred-batch reactor method at constant pH. When a column containing chitosan was used to bind Cr 6ϩ in a situation where pH could not be held constant because of pH changes caused by the chitosan itself, significant binding occurred only at solution pH 1 and 2. When chitosan was pretreated with sulfuric acid in a range of 7-70 mol % sulfuric acid : moles glucosamine residue, maximum binding occurred at pH 6.0. Under these conditions, a column containing 0.500 g acidtreated chitosan (35% mole ratio) reduced the concentration of Cr 6ϩ in 713 bed volumes of 25 ppm Cr 6ϩ solution to Յ5 ppm in the effluent. A similar column of pretreated chitosan reduced Cr 6ϩ concentration in 1042 bed volumes of industrial chromium plating rinse water initially containing 18 ppm Cr 6ϩ to Յ5 ppm. Capacity experiment results indicated 60 mg chromium bound per gram of treated chitosan at pH 6.0. Commercial resin IRA-67 was also investigated as a Cr 6ϩ binding agent.