Abstract:

Yangzonghai Lake in Kunming was heavily polluted by arsenic with concentration up to 0.134 mg/L. Through taking full account of the large water storage capacity and the low arsenic concentration, a facile generic strategy of removal of arsenic by ferric salt was proposed. The strategy was of great advantage for high efficiency, low cost and ecological safety. Experiments in the laboratory scale demonstrated that FeCl₃ coagulation can remove both As(Ⅲ) and As(Ⅴ) efficiently. Meanwhile, pH value of the water was kept constant after the coagulation process. Therefore, the pretreatment operations of pre-oxidation and adjusting pH value, which were widely employed in literature, were omitted in the treatment engineering for arsenic contamination of Yangzonghai Lake. Solid of FeCl₃·6H₂O was dissolved and diluted to prepare FeCl₃ solution with concentration of 1% FeCl₃, which was sprayed into the lake. Colloid of Fe(OH)₃ formed in the FeCl3 hydrolysis process would co-precipitate with ions of AsO^3-₄and AsO^-₂ in the lake and the stable precipitate was fixed in the sediment of the lake. During the treatment engineering for arsenic contamination of Yangzonghai Lake, the arsenic concentration was decreased from 0.117 mg/L to 0.021 mg/L in the period of November 2009 to September 2010. The concentration of arsenic could be kept below the national standard of category Ⅱ-Ⅲ (<0.05 mg/L) and the removal ratio of arsenic was up to 82.05%. Residual fraction was the overwhelming arsenic form in the lake sediment and its ecological risk was quite low due to its high stability.

Key words: arsenic removal, Yangzonghai Lake, ferric choride, engineering treatment