Copper removal from an effluent generated by a plastics chromium-plating industry using a rotating cylinder electrode (rce) reactor

Environmental Technology, Vol. 29. pp 817-825

© Taylor & Francis, 2008

COPPER REMOVAL FROM AN EFFLUENT GENERATED BY A PLASTICS CHROMIUM-PLATING INDUSTRY USING A ROTATING CYLINDER ELECTRODE (RCE) REACTOR
F. F. RIVERA, I. GONZÁLEZ AND J. L. NAVA*

Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Química Av. San Rafael Atlixco No. 186, C. P. 09340, México D. F., MexicoTaylor and Francis

(Received 16 May 2007; Accepted 25 November 2007 )

10.1080/09593330801987327

ABSTRACT This work shows the application of a rotating cylinder electrode (RCE) in the removal of Cu(II) content from an effluent generated by a plastics chromium-plating industry, on the laboratory scale; in particular, it deals with rinse water from the electrolytic copper process. This processwas designed to convert cupric ions in solution to metal powder. The generation of metal powders in the RCE was achieved at Reynolds numbers between 52925 and 83183 and limiting current densities (JL) in the range of 17 to 25 mA cm−2. The removal of Cu(II) (initially 922 ppm) reached 43 ppm in 10 minutes of electrolysis for Re = 83183 and J = 25 mA cm −2, with a space-time yield of 88 mg Cu(II) L−1min−1, 95% current efficiency, and energy consumption of 5.3 KWh m −3. The electrochemical treatment applied to waste rinse water at the RCE allows this treated water to be recycled back to the same rinsing process, avoiding additional consumption and discharge of this liquid.

Keywords: Rinse wastewater, copper deposition, powdery deposits, metal ions removal

INTRODUCTION

The plasticschromium-plating industry generates great amounts of aqueous effluents which contain heavy metals in solution originating from the rinsing of plasticcoated items. The removal of these metals is traditionally carried out by physicochemical methods where different metals are precipitated as hydroxides, generating large amounts of sludge that need to be subsequently confined. Despite this treatment,solubility limits of heavy metals, in many instances, exceed those allowed by environmental legislation. Electrochemical technologies have recently attracted attention, for they allow metal recovery in its most valuable form, that is, a zero-oxidation state, without requiring addition of chemicals, and thereby not generating by-products which would later require treatment or confinement [1–4].Moreover, electro-recovered metals, and waters treated using these electrochemical methods, can be reused in the same process, which is more economic and reduces water consumption and environmental impact. The electrochemical reactor with rotating cylinder electrode (RCE) is one of the most frequently employed technologies for metal removal, because it removes metals from 10 to 10,000 ppm [3, 5]. Forinstance, it has been used for recycling

zinc from solutions obtained in mining processes [6], for tin and cadmium recovery [7–9], for photo silver recovery [10], and for removal of copper contained in effluents [11]. One of the advantages of RCE in the cathodic recovery of heavy metal ions is to allow the generation of metal powders that are continuously coming off the rotating electrode,making possible fast removal kinetics. The formation of metal powders is achieved by applying a limiting current density to the RCE and by rotating the cylinder under turbulent flow conditions [12–15]. In a previous paper, Rivera and Nava [12] characterized mass transport at the RCE during copper powder generation on it, and established the following correlation:
Sh = 0.014 Re 0.91 Sc 0.356 (i)This correlation was obtained in a laboratory RCE using six plates as counter electrode. The value of the coefficient, 0.014, is associated with shape and cell dimensions, whereas the exponent of Reynolds number (Re), 0.91, is attributed to the combination of a higher surface area of the RCE and improved microturbulence at the roughened RCE interface. The difference between this correlation and...