Activated carbon adsorption of cyanide complexes and thiocyanate ion from petrochemical wastewaters

Experimental isotherms indicate that thiocyanate and nickel cyanide complex (tetracyanonicklate (II)) adsorb to an equal extent from synthetic and actual waste solutions at loadings below 10 mg/g carbon. Loading of nickel hexammine complex is an order of magnitude less. Adsorption of the divalent nickel cation is strongly pH dependent and is believed to be a chemisorption by precipitation or reaction on the carbon surface. In pure solution, ferrocyanide (hexacyanoferrate (II)) adsorption was comparable to that of thiocyanate or nickelocyanide, but adsorption from the waste liquor tested was negligible. This difference may be due to solvation of ferrocyanide with methanol in the wastewater to form a species with entirely different adsorption characteristics. Chemical oxygen demand (COD) values were obtained for several of the pure materials (SCN^?, 1.1; Fe(CN)₆^?4, 0.5; Ni(CN)₄^?2, 0.4 mg $\text{COD}\text{mg}$ ion) and the wastewater to monitor adsorption of organic background materials.