Surface modification of mixed sorbents with sulfide ions for purification of galvanic wash water of copper plating process

Abstract

Galvanic wastes are the main source of heavy metals entering the environment and irrational use of water as a technical resource. In order to rationally use purified water in closed production cycles and reuse removed/regenerated metals, it is important to study and implement local systems of rinsing water in electrochemical production. The complex water purification of copper plating of galvanic and sulphide-alkaline wastewater of petrochemical productions with the use of regenerated mixed sorbent (AC + K) depending on the order of modification of the sorption surface and pH of the initial medium has been investigated: method A, modification of copper (II), pH = 1.5-2.5; method B, sulfide-hydrosulfide modification of copper (II), pH = 12.6-13.2, as well as the concentration of the original sulfide-alkaline solution. A method of topochemical purification of galvanic copper flushing waters from copper (II) ions is proposed. It was found that the primary sorption of sorbents/ions Cu2+, S2-, HS- has a selective character, is determined by morphology, heterogeneity and the presence of active centers on the surface of the studied sorbents and therefore has a different investigated adsorption sequence. The obtained data indicate a slight adsorption of Cu2+ on the matrix surface, which is explained by both the nature of the adsorbate and the morphology of the adsorbent (AC + K) after its acid-base activation. It is obvious that the mixed microporous sorbents (AC + K) studied by us show cation exchange properties. Mainly carboxyl groups carry out sorption/binding of Cu2+ ions. It was found that the maximum sorption of copper (II) ions on the matrix surface, which has a small number of acidic carboxyl groups, takes place in a strongly acidic medium at pH = 1.5-2.5. Preliminary modification of the surface of sorbents (AC + K) with more active sulfide and hydrosulfide ions leads to a significant increase in its selective adsorption relative to copper (II) ions. Modification of the surface of mixed sorbents (AC + K) with sulfur-containing ions (S2-, HS-) allowed increasing the degree of extraction of copper (II) cations from the washing galvanic waters of the copper-plating process by 51.9%. Adsorption of sorbents by method A or method B begins with the formation of a sorption complex between the sorbate (Cu2+, S2-, HS-) and the primary activated center of the sorbent (AC + K). Taking into account the possible catalytic influence of the surface of activated carbon on the passage of topochemical transformations, the change of the valence-coordination node CuO2S2(H2O)2 will take place with the formation of the intermediate [CuS2]. It was found that topochemical reactions of formation of copper (II) CuSx polysulfides (x=2,3) take place on the surface of activated carbon, followed by their disproportionation to copper (II) sulfide and elemental sulfur. IR spectral and X-ray phase studies have established the possibility of undergoing topochemical transformations.The obtained results allow to recommend modification of carbon sorption materials with sulfur-containing ions (S2-, HS-) for more complete sorption extraction of Cr3+, Fe2+, Fe3+, Pb2+, Cd2+, Cu2+, Ni2+, Co2+, Zn2+ ions or their binary mixtures. It has been envisaged to use mixed sorbents (AC + K) with sulfur and copper (II) sulfide sorbed on their surface as components of special purpose greases.