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A comparative study on treatment of impure acid with low-concentration arsenic

Keywords: lime neutralization,lime-ferric flocculation,arsenic removal

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The arsenic removal efficiency from low concentration acid wastewater was evaluated by lime neutralization and the combination of lime with ferric iron in the present study. It was found that the level of arsenic, copper, lead and zinc could satisfy the limits specified by the hazardous waste discharge standard (GB 5085.3-2007) leached out of the arsenic-containing solid waste from the combination of lime with ferric iron treatment process. Therefore, the combined utilization was the preferred process because of its higher efficiency and innocuous compared with single lime neutralization. The corresponding parameters were also evaluated to achieve the optimized arsenic removal efficiency. The results indicated that the acid solutions were neutralized with lime in two hours to a final pH value of 2 in the first stage; the second-stage involved with Ca(ClO)2 oxidation with a Ca(ClO)2/As molar ratio of 6, ferric flocculation with a Fe/As molar ratio of 8, and lime neutralization to a final pH of 8 within an hour. After the two stages, the residual concentration of arsenic could below the tolerance level (0.3 mg/L) without any hazardous precipitates. The orthogonal design showed that the significance of the contribution of the above four factors to arsenic removal is ranked as: final pH of reacted solution > reaction time > Fe/As mole ratio > content of oxidant.


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