电镀废水中低浓度镍和锌离子的高效富集研究

电镀废水中低浓度重金属离子的处理普遍采用混凝沉淀法,由此产生了大量重金属污泥,其安全处置过程复杂且成本较高.基于此,本文研究了一种资源化回收电镀废水中低浓度镍离子(Ni~(2+))和锌离子(Zn~(2+))的方法.结果表明,电镀废水经过铁盐混凝后,产生的沉淀溶解于硝酸中,得到硝酸溶解液中Ni~(2+)和Zn~(2+)浓度分别高达2.3 g·L~(-1)和1.5 g·L~(-1),而杂质铁(Fe~(3+))浓度为12.2 g·L~(-1).将硝酸溶解液直接进行水热处理,溶液中Ni~(2+)和Zn~(2+)浓度不变,残留铁浓度为1.76 g·L~(-1).向硝酸溶解液中添加乙酰丙酸(C_5H_8O_3)后进行水热处理,Ni~(2+)和Zn~(2+)浓度依然不变,但溶液中残留铁浓度仅为0.78 mg·L~(-1).硝酸溶解液中铁的去除主要源于水热条件下铁的水解和缩聚转化为高结晶度的赤铁矿.添加乙酰丙酸能够同时降低溶液中NO~-_3浓度和提升pH值,促进溶液中铁的水解和缩聚.

A novel application of hematite precipitation for high-purity enrichment of nickel and zinc from smelting wastewater

Smelting wastewater was commonly treated with coagulation by adding polymeric aluminum to remove heavy metals, which generated considerable heavy metals-containing sludge that needs for proper treatment before safety disposal. Herein, we demonstrated a novel method to recycle nickel and zinc from smelting wastewater via a coupled coagulation and hydrothermal route. The smelting wastewater contained 11.3 mg·L^-1 Ni²⁺ and 7.2 mg·L^-1 Zn²⁺, and when adding polymeric iron coagulant, precipitates was formed, followed by the dissolution of precipitates in nitric acid solution. After dissolution, the nitric acid solution (short for solution) contained 2.3 g·L^-1 Ni²⁺, 1.5 g·L^-1 Zn²⁺ and 12.2 g·L^-1 Fe³⁺. After hydrothermal treatment, the Ni²⁺ and Zn²⁺ kept unchanged in the solution, while Fe³⁺ concentration decreased to 1.76 g·L^-1. The solution was further hydrothermally treated with the addition of acetylpropionic acid, and the Ni²⁺ and Zn²⁺ kept almost constant, but the concentration of residual Fe was only 0.78 mg·L^-1, and thus a high-purity of Ni²⁺ and Zn-containing solution was generated. The major mechanism for Fe³⁺ removal in the solution was hydrolysis, followed by polymerization of ferric Fe³⁺ into hematite, which was promoted by the redox reaction between acetylpropionic acid and nitrate, resulting in a low nitrate concentration and a high pH.