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Title: Application and investigation of chemical precipitation method for chromium removal and its recovery in one of the leather industries in Ethiopia.
Authors: Fenta, Minas
Advisors: B.S. Chandravanshi(Prof.)
Seyoum Leta(Dr.)
Keywords: Chromium,
removal
recovery,
chemical precipitation
tannery wastewater
Copyright: Apr-2011
Date Added: 12-Jul-2012
Publisher: Addis Ababa University
Abstract: Most tanneries in Ethiopia (90%) do not treat and very few (10%) partially treat their effluent before discharging it into the receiving water bodies, therefore, untreated leather effluent causes tremendous pollution of water resources in the country, especially due to its high organic loading and chromium content. Thus, proper treatment to eliminate or reduce the problem has to be devised. The purpose of this study performed at Addis Ababa Tannery Sh.Co. was to develop an alternative technical process for removing and recovering trivalent chromium from tannery wastewater via chemical precipitation. 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 is necessary for environmental protection and economic reasons. To 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. Flame atomic absorption spectroscopy (FAAS) method was used to determine Cr concentration. The results NaOH(99.973%), Ca(OH)2(99.97% ) and MgO( 99.98%) showed that removal efficiencies at optimum pH values were not significant. However, there is significant difference in sludge characteristics with sludge volume of NaOH (590 mL), Ca(OH)2(412 mL) and MgO(85 mL). The optimum pH is 9.8-10.3 with removal efficiency of 99.98% and the good sludge with high settling rate and lower volume was obtained by MgO precipitating agent. Hence the MgO is a good precipitating agent for removal and recovery of chromium from tanning wastewater. The basic chromium sulfate (BCS) recovered at pH 2.8 is suitable for tanning mixed with fresh BCS from the market.
Description: A Thesis Submitted to the School of Graduate Studies Addis Ababa University In Partial Fulfillment of the Requirement for the Degree of Master of Science in Environmental Science
URI: http://hdl.handle.net/123456789/3339
Appears in:Thesis - Environmental Sciences

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