Palden Thupten, Machiels Lieven, Onghena Bieke, Regadío Mercedes, Binnemans Koen
KU Leuven, Department of Chemistry Celestijnenlaan 200F, P.O. box 2404 B-3001 Leuven Belgium
SIM vzw Technologiepark 935 B-9052 Zwijnaarde Belgium.
RSC Adv. 2020 Nov 18;10(69):42147-42156. doi: 10.1039/d0ra08517k. eCollection 2020 Nov 17.
Ethylenediaminetetraacetic acid (EDTA) has been widely used as an effective reagent for removal of lead from soil because of its high lead extraction efficiency caused by the high thermodynamic stability of the Pb(ii)-EDTA complex. In this study, EDTA was used as a lixiviant for recovery of lead from residues (matte and slag) of secondary lead smelter plants. The residues were composed mainly of iron (34-66 wt%) and lead (7-11 wt%). Leaching parameters (EDTA concentration, pH, temperature, liquid-to-solid ratio and leaching time) were optimized. The optimum leaching efficiency was achieved when leached for 1 h at room temperature using 0.05 mol L EDTA at a liquid-to-solid ratio of 5 mL g. At such conditions, 72 to 80% of lead and less than 1% of iron were leached from both matte and slag. The high selectivity towards lead with minimal co-dissolution of iron is a major advantage since it reduces the chemical consumption and simplifies the downstream processes. Although the stability constants of the complexes Fe(iii)-EDTA, Fe(ii)-EDTA and Pb-EDTA are all large (log 25.1, 14.33 and 18.04, respectively), the leaching of iron was most likely limited by its presence in insoluble phases such as iron oxides, sulfides and silicates in the residues. 100% leaching of lead was achieved by a multi-step leaching process where the leaching residues were contacted three times by a fresh EDTA solution. To recover EDTA, first iron was precipitated as iron hydroxide by raising the pH of pregnant leach solution (PLS) above 12.6 using sodium hydroxide, followed by precipitation of lead as lead sulfide by adding ammonium sulfide. The recovered EDTA was successfully reused two times for leaching without significant changes in leaching yields.
乙二胺四乙酸（EDTA）因其形成的Pb（ii）-EDTA络合物具有较高的热力学稳定性，从而具有较高的铅萃取效率，已被广泛用作从土壤中去除铅的有效试剂。在本研究中，EDTA用作浸出剂，从二次铅冶炼厂的残渣（冰铜和炉渣）中回收铅。这些残渣主要由铁（34-66 wt%）和铅（7-11 wt%）组成。对浸出参数（EDTA浓度、pH值、温度、液固比和浸出时间）进行了优化。在室温下，使用0.05 mol/L EDTA，液固比为5 mL/g，浸出1 h时，可达到最佳浸出效率。在这种条件下，冰铜和炉渣中72%至80%的铅被浸出，铁的浸出率低于1%。对铅具有高选择性且铁的共溶解量最小是一个主要优点，因为它减少了化学消耗并简化了下游工艺。尽管Fe（iii）-EDTA、Fe（ii）-EDTA和Pb-EDTA络合物的稳定常数都很大（分别为logβ 25.1、14.33和18.04），但铁的浸出很可能受到其在残渣中不溶性相（如铁氧化物、硫化物和硅酸盐）中的存在的限制。通过多步浸出工艺实现了铅的100%浸出，其中浸出残渣与新鲜的EDTA溶液接触三次。为了回收EDTA，首先通过用氢氧化钠将富浸出液（PLS）的pH值提高到12.6以上，使铁沉淀为氢氧化铁，然后加入硫化铵使铅沉淀为硫化铅。回收的EDTA成功地重复使用了两次进行浸出，浸出率没有显著变化。
