Extraction and recovery of chromium from electroplating sludge
Paula Tereza de Souza e Silva a,∗ , Nielson Torres de Mello b , Marta Maria Menezes Duarte c , M. Conceicao B.S.M. Montenegro d , ¸˜ d , Ben´cio de Barros Neto a , Valdinete Lins da Silva b Alberto N. Ara´ jo u ı
Departamento de Qu´mica Fundamental, Universidade Federal dePernambuco, Cidade Universit´ ria, 50740-250 Recife-PE, Brazil ı a Departamento de Engenharia Qu´mica, Universidade Federal de Pernambuco, Rua Teresa Melia, s/n Cidade Universit´ ria, 50740-250 Recife-PE, Brazil ı a c Funda¸ ao do Instituto Tecnol´ gico do Estado de Pernambuco-ITEP, Av. Prof. Luiz Freire, 700 Cidade Universit´ ria, 50740-540 Recife-PE, Brazil c˜ o a d REQUIMTE/Dep. Qu´mica-F´sica,Faculdade de Farm´ cia, Rua An´bal Cunha 164, 4099-030 Porto, Portugal ı ı a ı Received 7 April 2005; received in revised form 15 July 2005; accepted 16 July 2005 Available online 6 September 2005
Abstract This work reports a study of the extraction and recovery of chromium from the wastes (class I dangerous) generated by a galvanic manufacturer. Commercial HCl at room temperature wasemployed, and the conditions of the extraction process were optimized according to a sequential experimental design, which also included the acid concentration and contact time as variables. The best extraction conditions (80% v/v; 30 min; 97.6% Cr) for the chromic sludge were chosen in order to make the recovery process economically feasible. After each extraction, the residue was submitted to leachingessays, to assess environmental risks. It was found that sludge could be characterized as no longer dangerous. In the recovery study, a simple and low-cost technique was evaluated for selectivity based on an oxidation step with hydrogen peroxide. A 23 factorial design to assess the inﬂuence of oxidation time (min), temperature (◦ C) and peroxide amount (mol/L) was employed. The best conditions,yielding a chromium recovery of about 92%, were a time of 60 min, a temperature of 60 ◦ C and 2.1 mol/L peroxide. Additional essays revealed that the same result could be obtained with more economic conditions (40 min, 1.4 mol/L peroxide and 60 ◦ C). This technique proved not only effective in comparison with existing alternatives, but also low costing. © 2005 Elsevier B.V. All rights reserved.Keywords: Galvanic manufacturing; Wastes; Chromium; Extraction; Recovery
1. Introduction Residues discarded by industrial processes ﬁgure among the most important sources of environmental contamination. This is especially true of processes that use or yield dangerous chemicals, leading to potentially dangerous residues . Many noxious residues are routinely treated for removal and recovery ofheavy metals, with techniques that include conventional neutralization or precipitation, electrochemical reduction, ion exchange, reverse osmosis, membrane separation, and solvent extraction [2–4]. Precipitation of metal ions as hydroxides, under appropriate pH conditions, has been one
Corresponding author. Tel.: +55 81 21267290; fax: +55 81 34232547. E-mail addresses: firstname.lastname@example.org (P.T.de Souza e Silva), email@example.com (V.L. da Silva). 0304-3894/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2005.07.026
of the most used conventional methods . This treatment, however, generates a heavy metal laden ‘slime’ or ‘sludge’. The literature reports only few works on heavy metal recycling, and is scarce concerning chromium found in sludgeresulting from chemical neutralization and precipitation. Since recovery of these metals with traditional separation procedures does not appear to be economically feasible, a search for safe alternative solutions for their ﬁnal disposition is warranted . One such possibility is using the metal sludge as an additive to cements and ceramic materials [7,8]. The main drawback of this approach...