基于无定形砷酸铁沉淀的铜冶炼污酸除砷研究

Study on Gradient Arsenic Removal from Waste Acid of Copper Smelting Based on Amorphous Iron Arsenate Precipitation

针对传统石灰-铁盐污酸处理工艺产出的中和渣含砷高、不能进入柔性填埋场堆存的现状,采用基于无定形砷酸铁沉淀的预中和-铁盐沉砷方法,降低石灰-铁盐污酸处理流程中和渣砷含量,确保含砷渣能够进入柔性填埋场。热力学分析发现,砷酸铁稳定存在的pH值为0~5.2;在pH=4~5时,As-Fe-H_(2)O体系中砷酸铁可以形成并稳定存在,同时不会产生Fe(OH)_(3)沉淀。研究表明,石灰乳预中和过程终点pH为4.5时,没有砷酸钙沉淀产生或少量产生,预中和石膏含砷小于3%。铁盐沉砷过程温度和初始pH值的升高,有利于降低沉砷后液As浓度、增加As沉淀率和沉砷渣中As含量;但提高初始铁砷摩尔比和初始砷浓度,并不利于砷的沉淀。在低温(40℃)及较短的时间(1h)的条件下,单独采用空气或者80%氧气作氧化剂,难以获得较好的沉砷效果,必须加入适量的H_(2)O_(2),以提高As^(3+)离子的氧化效率。在优化条件下,沉砷后液平均砷浓度为2.80g/L,沉砷渣平均含砷27.01%,沉砷渣为疏松多孔的无定形砷酸铁,砷沉淀率为71.62%。沉淀反应是无定形砷酸铁生成过程的限制步骤。

In view of the current status that the arsenic content in the neutralization slag from traditional lime neutralization Fe-As coprecipitation technology is high,and it cannot be stored in flexible landfill,a lime milk preneutralization-ferrite slat precipitation method based on amorphous iron arsenate precipitation was used to lower the arsenic content in the neutralization slag obtained from the traditional technology to guarantee the neutralization slag be stored in flexible landfill in this work.This method will resolve the problem of high arsenic content in the neutralization slag at the front of the traditional technology.Most of the arsenic will be removed from waste acid in the form of amorphous iron arsenate which can be further disposed by returning to copper melting furnace.The solution after arsenic precipitation was treated by sending to the traditional technology.The effects of temperatur and final pH value in lime milk preneutralization process,and temperature,initial pH value,initial molar ratio of iron to arsenic,arsenic concentration,as well as type and dosage of oxidant in ferrite slat precipitation process on arsenic precipitation efficiency were investigated.The iron arsenate is stable under the pH value of 4.5—5.0and iron hydroxide doesn′t form during arsenic precipitation process.The results showed that no calcium arsenate precipitates or small amounts were produced when the final pH value was 4.5in the lime milk preneutralization process,and the arsenic content in preneutralization gypsum was less than 3%.The arsenic concentration in the solution after arsenic precipitation should decrease and arsenic precipitation efficiency and arsenic content in iron arsenate precipitation should increase with an increase of temperature and initial pH value during arsenic precipitation process using iron salt.However,it was unfavorable to the precipitation of arsenic by increasing initial Fe/As molar ratio and arsenic concentration.The oxidation rate of arsenic is slow under acidic conditions.It was difficult to obtain high arsenic precipitation efficiency using air or 80%oxygen as an oxidant.An appropriate amount of H_(2)O_(2) must be added to improve the oxidation rate of As(Ⅲ)ions.The arsenic concentration in the solution after arsenic precipitation,arsenic concentration in iron arsenate precipitation,and arsenic precipitation efficiency were 2.80g/L,27.01%and 71.62%respectively under optimized conditions.The formation process of amorphous iron arsenate was controlled by precipitation reaction rate.