Specific resins for metal ion separation. The Cr(III), Fe(III), Al(III) system

Among established technologies for metal control in the environment it is worth iftentioning selective ion exchange, membrane separation, and electrolysis. Ion exchange, in particular, seems to offer additional advantages over environmental operation in terms of separation and reuse of valuable metallic by-products. In reference to specific ion exchange applications, however, insufficient literature data are available and this is particularly true for some multivalent ionic systems, thus making the theoretical prediction of the general behaviour of resins towards reference systems difficult. In this paper data are presented and discussed relative to the separation of Cr(III), Fe(III)& Al(III) by means of a process based on the use of selective reactive polymers. Starting from a complex mixture of the three metals and organic chelating agents, simulating the sulphuric acid extract of a typical tannery sludge, metal separation and recovery is achieved by means of a simple set-up. A weak base resin (Duolite A-7), as “specific” chelating agent for the Fe(III) complex, and a strong cation resin (Purolite C 160), for “selective” separation of Al(III) from Cr(III) complex, are efficiently used to the purpose. Details for separation of ionic species based on their speciation in the liquid-phase are given.