含砷废水制备三氧化二砷的工艺研究

Technique for Preparation of Arsenic Trioxide from Ascontaining Wastewater

探索了以含砷废水为原料,经过砷酸钙沉淀转化,硫酸浸出以及亚硫酸还原等步骤制备三氧化二砷的研究。研究结果表明,氧化钙沉砷的最佳工艺条件为:p H=12.0,Ca/As摩尔比为3.0,反应温度85℃,反应时间3 h,搅拌速度250 rpm。在此条件下,砷的沉淀率达到99.95%,沉砷后液中的砷降到2.2 mg/L。硫酸浸砷的最佳工艺条件为:硫酸过量系数为1.2、浸出时间1.5 h、浸出温度为90℃、液固比为6、搅拌速度500 rpm。在此条件下,砷的浸出率达到99.98%,渣中含砷率低于0.5%。往浸出液中加入理论量1.5倍的亚硫酸,在搅拌条件下还原2.5 h,得到还原溶液。还原溶液经浓缩、冷却结晶、过滤得到三氧化二砷粗产品。粗产品再经过重结晶,得到精制三氧化二砷产品,其成分符合国家三级标准。

An investigation was made on preparing arsenic trioxide with As-containing wastewater as raw material by means of calcium arsenate precipitating, sulphuric acid leaching and sulphurous acid reduction. The results show that the optimum conditions of precipitation process are as follows： pH value of 12.0, molar ratio of Ca/As of 3.0, reaction temperature of 85~C, reaction time of 3hrs and agitation speed of 250 rpm. Under the optimum conditions, As precipitation rate is 99.95% while As content in the precipitated solution decreases to 2.2 mg/L. The optimum conditions for As leaching by sulfuric acid are as follows： sulfuric acid excess coefficient of 1.2, leaching time of 1.5 h, leaching temperature of 90~C, solid-liquid ratio of 6 and agitation speed of 500 rpm. Under the optimum conditions, leaching rate of arsenic is 99.98% while arsenic content in the leaching slag is less than 0.5%. Sulfurous acid, at a dosage of 1.5 times of the theoretical amount, is added to the leaching solution and reduced for 2.5 hrs with stirring. Then, reduced solution is obtained. Crude product of arsenic trioxide is obtained by concentration, cooling crystallization and filtration of the reduced solution. After re-crystallization of the crude product, refined arsenic trioxide is obtained, reaching the Grade II national standard.