Journal of Hazardous Materials 176 (2010) 710–714 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Production of basic chromium sulfate by using recovered chromium from ashes of thermally treated leather Aline Dettmer a,∗ , Keila Guerra Pacheco Nunes a , Mariliz Gutterres b , Nilson Romeu Marcílio a,∗ a Department of Chemical Engineering, Laboratory of Wastes Treatment (LPR), Federal University of Rio Grande do Sul, Luiz Englert str., s/n ◦ , 90.040-040, Porto Alegre, RS, Brazil b Department of Chemical Engineering, Laboratory for Leather and Environment Studies (LACOURO), Federal University of Rio Grande do Sul, Luiz Englert str., s/n ◦ , 90.040-040, Porto Alegre, RS, Brazil article info Article history: Received 3 August 2009 Received in revised form 16 November 2009 Accepted 17 November 2009 Available online 24 November 2009 Keywords: Ashes Sulfate Leather Wastes Chromium recovery abstract Leather wastes tanned with chromium are generated during the production process of leather, hence the wastes from hand crafted goods and footwear industries are a serious environmental problem. The thermal treatment of leather wastes can be one of the treatment options because the wastes are rich in chromium and can be used as a raw material for sodium chromate production and further to obtain several chromium compounds. The objective of this study was to utilize the chromium from leather wastes via basic chromium sulfate production to be subsequently applied in a hide tanning. The obtained results have shown that this is the first successful attempt to achieve desired base properties of the product. The result was achieved when the following conditions were applied: a molar ratio between sodium sulfite and sodium dichromate equal to 6; reaction time equal to 5 min before addition of sulfuric acid; pH of sodium dichromate solution equal to 2. Summarizing, there is an opportunity to utilize the dangerous wastes and reused them in the produc- tion scheme by minimizing or annulling the environmental impact and to attend a sustainable process development concept. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The activities related to leather and footwear industry processes have a high impact on the environment due to the high quan- tity of process residues. The wastes are classified as dangerous by the Brazilian Legislation, mainly due to the presence of chromium. Moreover, effluents and pollutants are generated from different sources (gases, liquids and solids) during the multi-step leather process. The disposal of these residues is a concern because their accu- mulation in the environment has increased during the years. The search of alternatives for re-use, recycling, treatment and correct disposal has been the focus of much research. According to Vieira [1], approximately 300 tons per day of wastes containing shavings of leather are generated in Brazil. One of the alternatives to utilize these wastes is the thermal treatment. The ashes formed in the process can be used as a raw material to obtain sodium chromate, which is the production precursor of a basic chromium sulfate (BCS), salt widely used in the hide tanning. Due to a high concentration of chromium oxide (between 40 and ∗ Corresponding authors. Tel.: +55 51 3308 3956; fax: +55 51 3308 3277. E-mail addresses: alinedet@enq.ufrgs.br (A. Dettmer), nilson@enq.ufrgs.br (N.R. Marcílio). 50% of Cr 2 O 3 ) in the ashes obtained after the thermal treatment, this material can be used as a chromite substitute. It is desirable to recover chromium ashes and reused them in the leather tanning process, through a basic chromium sulfate. The basic chromium sulfate production includes a step of hex- avalent chromium reduction. According to Udy [2], a careful acidity adjustment, dilution (concentration) and molar ratio between reduction agent and dichromate are important variables of a basic chromium sulfate production process, where the final product may reach excellent tanning characteristics. Basicity is considered a determinant feature of basic chromium sulfate with an excellent tanning power. The basicity indicates the number of hydroxyls radicals attached to the chromium atom. An increase of basicity decreases the diffusion of salt, but increases the fixation to the hide. There are salts with different basicities in the market such as 33%, 40%, 48% and 50%, respectively. The most utilized chromium salts in hide tanning have basicity of 33% or less, in order to guarantee the optimal chromium diffusion into the material and to avoid a superficial tanning. According to Covington [3], the basic chromium sulfate with basicity 33% has pH in solution about 2.8 and contains mostly bi- nuclear species, while the basic chromium sulfate solution with basicity 50% has pH about 3.5 and contains tri-nuclear species. In the work of Hoinacki et al. [4] to reduce chromium(VI) to its less mobile and toxic chromium(III) form, several reduction agents 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.11.090