Extraction of hazardous metals from green liquor dregs by ethylenediaminetetraacetic acid

Green liquor dregs are the major inorganic solid side stream of kraft pulp mills which contain environmentally hazardous metals. The presence of hazardous metals in this industrial residue brings statutory limits for its landfilling, although they are not easily mobilized from the solid phase. In this study, the chelating agent ethylenediaminetetraacetic acid (EDTA) is utilized to extract hazardous metals such as Cd, Pb and Zn from green liquor dregs. Furthermore, the influence of EDTA on the removal of Ca as the main mineral nutrient present in the green liquor dregs is studied. The effect of parameters such as EDTA dosage, L/S ratio and contact time on the removal rate of the elements is investigated. In addition, the experimental data are fitted to the Elovich model and the pseudo-first-order model to describe the desorption kinetics. The results show that 59 wt% of Cd, 13 wt% of Co, 62 wt% of Cu, 3 wt% of Mn, 12 wt% of Ni, 43 wt% of Pb, 16 wt% of Zn, and less than 1 wt% of Ca were extracted from green liquor dregs with EDTA dosage of 0.035 gEDTA salt/gdregs and the L/S ratio of 6.25 ml/g. The current study opens up new possibilities to use the green liquor dregs for improving the soil fertility instead of landfilling.