Optimization of a pertraction process for wastewater treatment and copper recovery

A. M. ELICECHE; M.F.ORLANDI; A.M.URQUIAGA; I. ORTIZ

Garmish, Germany

Simposio; 16th European Symposium on Process System Engineering - ESCAPE16; 2006

European Federation of Chemical Engineering

  Membrane contactors offer a cleaner alternative to the separation and recovery of many contaminants from polluted waters. The separation is carried out by avoiding mixing of the fluids. The analysis of an emulsion pertraction process (EPP) to extract and recover copper from wet peroxide oxidation (WPO) residual waters and concentrate simultaneously the copper in a product to be recycled and reused as homogeneous catalyst in the WPO process is presented. The amount of Cu disposed into the environment is practically eliminated. The aim of this study is to optimise this new and cleaner process at the conceptual design stage to evaluate the economical viability of its industrial application and eventually promote the use of this technology. Only one sector of membrane modules is required for the extraction and stripping processes against two sectors of membrane modules required in Non Dispersive Solvent Extraction process that also allows the recovery of copper. The economical incentive of EPP is that less membrane area is required and therefore less investment and operating cost than the NDSX process. The aim of this study is to optimise the operation of the EPP process analysing a copper concentration of wastewaters ranging from 100 to 1000 ppm, with the emulsion flow rate as the operating variable to be selected. The mathematical modeling is reported by Urtiaga et al (2005). The residual wastewaters circulates inside the hollow fiber while the emulsion run counter currently through the shell. The organic and stripping phases of the emulsion are separated in a decanter tank, the organic phase is reused to form a new emulsion. The extraction from the wastewaters into the organic phase of the emulsion is assisted with hollow fiber membrane modules while the back extraction from the organic into the stripping phase is carried out in the emulsion.  The copper mass transfer is described in four steps: (i) diffusion of copper ions in the feed phase through the liquid boundary layer; (ii) interfacial chemical reaction of copper cations with the organic extractant to form an organic-copper complex; (iii) diffusion of the complex through the organic phase impregnated in the porous membrane and (iv) interfacial chemical reaction of the complex with the back-extraction agent at the outer surface of the stripping phase globules of the emulsion. Equations describing the counter flux of hydrogen ions and free extractant compound are also considered. The differential and algebraic system of equations that model the mass transfer in the wastewaters, organic and stripping phases of the emulsion in the membrane modules are posed as equality constraints in the optimisation problem. The objective function is the maximization of the effluent flowrate treated in the EPP plant. The maximum allowed copper composition in the treated wastewaters for final disposal is 0.5 ppm and it is posed as an inequality constraint. A differential nonlinear programming problem is formulated and solved with gOPT of gPROMS. The improvements achieved and the sensitivity of the optimal operating conditions with respect to different wastewaters copper composition will be reported.   Urtiaga A., Abellán M.J., Irabien J.A. and I. Ortiz, Membrane contactors for the recovery of metallic compounds. Modelling of copper recovery from WPO processes, Journal of membrane Science 257 (2005), 161-170.