Research on the possibility of heavy metals separation from metallurgical wastes using an EDTA extraction and nanofiltration process

Zinc and lead metallurgy generate significant amounts of waste. Among the many types, a large percentage are slags and sediments. Separating heavy metals from wastes using simple processes can become particularly advantageous both because of the possible recovery of valuable components such as heavy metals, but also for environmental reasons. This work presents the results of the extraction process for selected heavy metals from metallurgical wastes (slag from the Short Rotary Kiln, slag from the hazardous waste landfill, and post-neutralization sludge) using ethylenediaminetetraacetic acid disodium salt (Na2EDTA) as a leaching agent. Because heavy metals removal from wastes using an extraction process generates large quantities of post-extraction solutions, the eluates were subjected to nanofiltration to investigate the possibility of metal concentration depending on the varying pH of the process. The metals present in the wastes in the largest amounts, whose removal was studied in the paper, were Pb, Zn, Cu, and Fe in the slag samples and Pb, Zn, and Cd in the post-neutralization sludge. The leaching agent concentration and pH of the extraction process were analyzed in terms of extraction process efficiency. The best efficiency of the leaching process was obtained using a leaching agent solution of 0.15 mol/dm3 for the slag from the Short Rotary Kiln and 0.075 mol/dm3 for the other tested samples. For all samples, the highest leaching efficiency was observed at pH = 4, obtaining high removal of Pb (80%), Zn (89%), and Cd (98%), and lower values of separation efficiency of Cu and Fe, not exceeding 30% and 21%, respectively. The use of the nanofiltration process allowed to obtain a high retention rate of metals. The removal efficiency was pH-dependent and the highest retention factor (98%) was obtained at pH = 4 and pH = 10.