Abstract
Chromium (III) salts are the most widely used chemicals for tanning processes, but 60-70% of total chromium salts reacts with the hides. In the other word, about 30-40% of the chromium amount remains in the solids and liquid wastes (especially spent tanning solutions). Therefore, the removal and recovery of the chromium content of these wastewaters are necessary for environmental protection and economic reasons. Removal and recovery of chromium were carried out by using precipitation process. For this purpose, three precipitating agents calcium hydroxide, sodium hydroxide and magnesium oxide were used. The effects of pH, stirring time, settling rate and sludge volume were studied in batch experiments. Results show that the optimum pH is 8-9 and the good sludge with high settling rate and lower volume obtain by the MgO precipitating agent. Hence the MgO is a good precipitating agent for removal and recovery of chromium from tanning wastewater.
Highlights
Chromium solutions are widely used in many industrial processes such as chrome plating, wood preserving, textile dyeing, pigmenting, Cr chemical production, pulp and paper industrial and tanning
The purpose of this research was to compare pH, velocity of precipitation, sludge volume, time of mixing and complexing agent when using the three precipitation agents in the precipitation process of the tannery waste water chromium. Wastewater resulting from these processes contains high amount of chromium metal which is harmful for the environment and human health [1,2]
The chemicals used in this research were raw wastewater from tanning process; solutions of lime, sodium hydroxide 15% and magnesium oxide 10%
Summary
Chromium solutions are widely used in many industrial processes such as chrome plating, wood preserving, textile dyeing, pigmenting, Cr chemical production, pulp and paper industrial and tanning. Wastewater resulting from these processes contains high amount of chromium metal which is harmful for the environment and human health [1,2]. Tanning process using chromium compounds is one of the most common methods for processing of hides[3]. In this process about 60% - 70% of chromium reacts with the hides. 40% of the chromium amount remains in the solid and liquid wastes (especially spent tanning solutions). The wastewater of the tanning process is an important source adding Cr pollutant to the environment. Hafez et al.[7] and Chaudry et al .[8] reported that the Cr ion concentration in the tanning wastewater varies from 2500 to 8000 ppm and 1300 to 2500 ppm, respectively[7,8]
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