材料期刊网

从热力学分析和试验两方面研究As(Ⅲ)在酸性水溶液中与金属铁的反应行为。热力学计算结果表明：在酸性水溶液中，As(Ⅲ)与金属铁作用，分别生成As元素或AsH 3气体的反应在热力学上均是可行的。试验结果表明：在温度为20~80℃、溶液初始pH值为?0.31~4、溶液初始浓度ρ[As(Ⅲ)]为1~20 g/L、铁粉大量过剩的条件范围内，由于动力学方面的原因，生成AsH 3的反应实际并不会发生，铁粉仅能使As(Ⅲ)还原为As元素。铁粉“过量”系数、溶液pH值和温度对沉砷率有显著影响，提高铁粉“过量”系数和温度，可使沉砷率增大，在溶液pH值为3的条件下，沉砷效果最佳。在酸性溶液中，铁粉置换As(Ⅲ)生成As的反应难以进行到底的原因，可能是由于还原的As在铁粉表面沉积阻滞了反应的延续。而在初始pH值为3或较高温度条件下能达到较高的沉砷率，是由于在这些条件下，置换的砷呈疏散形态沉积，未能对铁粉表面形成紧密包裹，使得反应得以延续。

The reactive behaviors between As(Ⅲ) and metallic iron in acidic aqueous solutions were investigated thermodynamically and experimentally. The thermodynamic calculation results show that the reactions between As(Ⅲ) and metallic iron in acidic aqueous solutions, which produce both elemental arsenic and AsH3 gas, respectively, are feasible thermodynamically. The experimental results show that, owing to the kinetic reason, the reaction producing AsH3 gas never occurs actually under a wide range of the conditions, such as, temperature from 20 to 80℃, initial solution pH value from?0.31 to 4, initial As(Ⅲ) concentration from 1 to 20 g/L, and a massive surplus in iron powders. Under these conditions, the iron powders can only reduce As(Ⅲ) ions from solution as elemental arsenic deposition. These factors, such as surplus coefficient of iron powders, solution pH value and temperature, all have obvious effects on the arsenic deposition rate. The arsenic deposition rate increases with the increase of the surplus coefficient of iron powders and temperature, while the best result of arsenic deposition rate is obtained when the pH value is 3. In acidic aqueous solutions, the reaction of iron powders replacing As(Ⅲ) is difficult to progress quickly to the end, the reason may be that arsenic reduced deposits on the surface of iron powders retard the reaction forward. Moreover, a higher arsenic deposition rate is obtained under the condition of pH=3 or higher temperature, the reason can be deduced that, under these conditions, arsenic deposits in loose form, and does not closely coat the surface of iron powders, thus making the reactions between As(Ⅲ) and iron powders sustainable.