Recovery of Phosphate Sludge as Concrete Supplementary Material

Abstract

The automotive industry plays a major role in the worldwide economy and represents an opportunity to increase the performance of the Turkish economy. Phosphating units in the automotive manufacturing plants generate phosphate sludge as waste, which is classified as hazardous waste in the European Waste Catalogue. Phosphate sludge must be disposed of in licensed disposal plants according to the current environmental regulations. Solidification/stabilization (S/S) is a widely used treatment technology for the disposal of hazardous wastes. Portland cement is used for the solidification and stabilization processes to immobilize Ni and Zn in the phosphate sludge as well as to create construction material to be used as cobble stone for pavement. Examination of products obtained by S/S processes is performed for two points: to determine the quality and to assess the environmental impacts. The phosphate sludge samples are subjected to chemical characterization and a size distribution analysis leaching test. Concrete for cobble stone was produced by the S/S process with the addition of phosphate sludge to replace sand. Tests for the quality of the product were carried out to determine compressive strength, permeability, and elasticity. At the end of the leaching test, elution concentrations of Zn and Ni while using water with pH values of 4.0, 5.4, and 9.0 were determined to be under the limit of inert material properties. Use of phosphate sludge should be considered as a sand replacement in the proportion of 1% of phosphate sludge to cement in concrete production, such as for cobble stone for pavement, without any adverse environmental impacts.

A safer disposal of hazardous phosphate coating sludge by formation of an amorphous calcium phosphate matrix

“…1500-1400 cm In connection with the toxic metals amounts, Cu, Mn, Ni, Cr and specially Zn were the most abundant hazardous metals found in the samples. These results are in good agreement with the results reported in previous works for similar wastes (Dogan and Karpuzcu, 2010;Ucaroglu and Talinli, 2012;Caponero and Tenório, 2000;Pinarli et al, 2005), as PS are mainly composed of zinc phosphates coming from decanter baths of phosphate, very commonly used in the industry responsible for this kind of wastes. Both sludges can be classified as hazardous wastes, due to their reactive and toxic characteristics according to the regulations and cannot be landfilled without a previous S/S process (Ucaroglu and Talinli, 2012).…”

“…In the reference sample, pure sodium hexametaphosphate (acidic compound) added quickly reacted with the CAC (basic compound) yielding a strong and low porosity matrix (Swift at al., 2013a;Fernández et al, 2014). Given that wastes are composed of lower percentages of phosphates and present heavy metals and organic matter, the strength reduction was an expected result, in good agreement with previous works on S/S processes of phosphate sludge into cement matrices (Dogan and Karpuzcu, 2010;Ucaroglu and Talinli, 2012;Pinarli et al, 2005). Comparatively, the BS induced a stronger reduction, which is in line with the more intense interference with the setting process observed for these samples.…”

“…The automotive industry originates wastes such as shredder residue (Péra et al, 2004), paint (Arce et al, 2010) or phosphate coating sludge (PS) (Dogan and Karpuzcu, 2010;Ucaroglu and Talinli, 2012). Phosphating is the most widely applied system for metal pretreatment process.…”

“…Of course, different operating parameters and in-process modifications could also render final wastes with diverse compositions and degree of health hazard. Nevertheless, within the field of automotive industry, PS has been often reported to be one of the most problematic varieties of waste, due to the possible leaching of the heavy and/or transition metals which contains (Dogan and Karpuzcu, 2010;Ucaroglu and Talinli, 2012). Accordingly, it has been classified as a hazardous waste by the U.S. Environmental Protection Agency (EPA) and the European Union.…”

“…Regarding the S/S treatment of PS, scarce studies have been reported in the literature. In all of them, authors have used ordinary Portland cement (OPC) as binder (Dogan and Karpuzcu, 2010;Ucaroglu and Talinli, 2012;Pinarli et al, 2005).…”