Investigation of the effect of Electrocoagulation operational parameters on the leachability of arsenic in sludge = Investigation of the effect of Electrocoagulation operational parameters on the leachability of arsenic in sludge
저자
발행기관
학술지명
권호사항
발행연도
2018
작성언어
-자료형태
학술저널
수록면
511-511(1쪽)
제공처
Mine drainage from gold mines abundant in sulphide ores is characterized by elevated arsenic (As) concentrations and other hazardous heavy metals such as Pb, Cd, Cu and Zn. Treatment of mine drainage generates tons of hazardous sludge enriched in these heavy metals. Disposal of wastewater treatment sludge requires specific attention due to the hazardous nature of the sludge. Electrocoagulation (EC) is increasingly being used for removing Arsenic (As), replacing conventional chemical coagulation due to its higher removal efficiency and lower costs. The process takes place in an electrochemical cell operated with Iron electrodes. Upon passage of current, dissolution of iron electrodes generates positively charged iron oxide/hydroxide complexes (Fe(H<sub>2</sub>O)<sub>6</sub><sup>3+</sup>, Fe(H<sub>2</sub>O)(OH)<sup>2+</sup>, Fe<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>(OH)<sub>4</sub><sup>4+</sup> and goethite FeO(OH)) with large adsorption surface areas. EC produces less sludge that is more stable, containing less bound water due to larger floe sizes and is easier to filter, however, the sludge may still be considered hazardous. This raises several questions pertaining to the effect of operational parameters such as initial pH, Initial As concentration on the stability of sludge. This study aims to investigate the effect of EC operational parameters on the leachability of As from sludge generated. In doing so, this would assist in optimizing the performance of the treatment that would yield the most possible benign waste.
Synthetic wastewater is prepared using concentrations of anionic and cationic constituents typically found in gold mine drainage. Laboratory scale EC experiments were conducted. At first, influence of initial concentration of arsenic on the leachability of As from the sludge generated was confirmed by conducting EC tests by changing the concentration (i.e. 10 and 100mg/l). Then, EC test by changing pH was conducted. In each test, pH was kept constant at 3, 5, 7, and 9, respectively. The aim of these tests was to investigate differences in leaching due to the phase of iron oxide/hydroxide generated at the specified pH. Leaching tests were conducted on the sludge obtained from each run. Residues from the leaching tests were acid digested and analyzed. Arsenic removal efficiency was very high for both initial As concentrations (99.5% for 10, and 95.0% for 100 mg/L).The amount of Iron oxide/hydroxide generated was the limiting factor. Test condition of lower initial concentration was able to remove As at a higher efficiency due to less competition for surfaces on the iron oxide/hydroxide phases generated. Differences were also observed in the amounts of As leached. Sludge obtained from an initial 10 mg.As/L sample leached a smaller amount of As compared to 100 mg.As/L indicating the importance of Fe/As molar ratio. For the runs conducted at constant pH, higher removal efficiency was observed in the order of pH=7, 5, 9, and 3. Removal efficiency was very high for all runs (above 99%). Similar results were identified when each sludge was subjected to leaching tests. The order of the fraction (by mass) remained in the sludge after the leaching test was pH= 7 > 5 > 9 > 3. This indicates that the iron oxide/hydroxide phases formed in situ at varying pH are bound to As at varying levels.
To ensure the generation of the most benign sludge possible, it is imperative to understand the interaction between operating conditions and sludge generated. Consequently, this research aims to farther investigate other operational parameters such as electrode gap and current applied. Additionally, a characterization of the sludge generated by SEM should also be conducted to elucidate on the phases formed.
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