不锈钢硫酸洗涤废酸中金属离子的草酸络合沉淀行为

Behaviors of metal complex precipitation with oxalic acid in waste sulfuric acid solutions from stainless steel washing processes

不锈钢表面处理常采用稀硫酸溶液预洗涤,洗涤过程产生大量含铁及其他微量元素的废酸。实际生产中废酸多采用中和方法进行处理,试剂耗量大,产生大量废渣,污染环境。针对典型不锈钢硫酸预洗涤过程中产生的废酸,研究废酸体系中草酸络合沉淀Fe(Ⅱ)、常见微量金属Cr(Ⅲ)、Ni(Ⅱ)以及Mn(Ⅱ)的行为,并探讨沉淀去除金属离子后废酸的循环利用。结果表明:随着废酸溶液中酸度的增高,金属沉淀率降低,但在起始H_2SO_4浓度<200 g/L、x(H_2C_2O_4):x(Fe(Ⅱ))摩尔比为1:1下,Fe(Ⅱ)的沉淀率仍达80%以上;金属离子的沉淀顺序为:Ni(Ⅱ)>Fe(Ⅱ)>Mn(Ⅱ)>>Cr(Ⅲ);金属离子沉淀后废酸溶液中酸度得到有效恢复,经x(H_2C_2O_4):x(Fe(Ⅱ))>0.75:1处理后的废酸对不锈钢表面氧化层具有较好的洗涤效果,实现了不锈钢洗涤废酸的再生循环利用。

Sulfuric acid solution was commonly used for the surface pre-washing in the process of stainless steel treatment to remove the metal oxide layer.Large amounts of waste acid solutions containing high concentrations of iron and low concentrations of other metals were discharged in the process.Neutralization method was widely used in industrial practices,resulting in high reagent consumption,large amounts of solid waste discharge and serious environmental pollution.With respect to the typical waste sulfuric acid solutions,the complex precipitation behaviors of Fe(II)and some commonly found trace metals,such as Cr(III)、Ni(II)and Mn(II),with oxalic acid were investigated.The recycling of acid solutions after metal removal was also discussed.The results show that the metal precipitation decreases with the increase of the acid concentration.As the initial acid concentration is less than 200 g/L,the precipitation of Fe(II)still reaches more than 80%.The metal precipitation order is:Ni(II)>Fe(II)>Mn(II)>>Cr(III).After metal removal by precipitation,the acid concentration in the solution increases,restoring the pre-washing effectiveness.The waste acid solutions are treated using H2C2O4:Fe(II)molar ratio higher than 0.75:1,good pre-washing effectiveness can be achieved.Therefore,the waste acid can be well recycled after metal precipitation using oxalic acid.