زدايش كروم )III( از پساب دباغي به وسيله فرآيند رسوب دهي

Chromium (III) Removal from Tannery Wastewater by Precipitation Process

Backgrond and Objective: Chromium (III) salts are the most widely used chemicals for tanning processes, but 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 is necessary for environmental protection and economic reasons. The aim of this study was chromiam removal from tannery wastewater by precipitation process. Materials and Methods: Removal and recovery of chromium were carried out by using precipitation process. To this purpose, three precipitating agents were used; calcium hydroxide [(Ca(OH)2)], sodium hydroxide (NaOH) and magnesium oxide (MgO). The effects of pH, stirring time, setteling rate and sludge volume were studied in batch experiments. Results: Results showed that the optimum pH was 8-9, and the setteling rate of the process for magnesium oxide was much more than this rate for the other two compounds. Furthermore, a grainy, dense, easly settelable precipitate could also be formed when MgO was used as the precipitator. Whereas, precipitates forming by NaOH was very gelatinous and the setteling rate was low. Precipitates forming by Ca(OH)2 was not also desirable. Sludgeʹs volume by MgO was much less than sludge volume produced by Ca(OH)2 and NaOH. Conclusion: The MgO is an effective and suitable precipitating agent for removal of chromium from tanning wastewater.