Recycling Phosphated Residue for Pb2+ Removal from Wastewater

Phosphated residue (PR), a common solid waste generated from iron and steel plants, was directly reused for removing Pb2+ from wastewater by adsorption. Effectiveness and mechanism of Pb2+ removal by PR were investigated by batch experiments. The toxicity characteristic leaching procedure (TCLP) test confirmed that PR was a nonhazardous material and could be used as an adsorbent for subsequent experiments. Studies of pH impact showed that the optimum pH for Pb2+ adsorption on PR was 5.2 ± 0.2. Kinetic studies illustrated that the sorption behavior of Pb2+ could be described better by pseudo-second order model with high correlation coefficient (0.9999). Sorption equilibrium data could be appropriately fitted by the Langmuir model and the maximum adsorption capacity of Pb2+ obtained from Langmuir equation was 151.2 mg/g. Results of X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive spectrum (SEM-EDS) analysis indicated that dissolution and precipitation mechanism predominated for the sorption. For fixed column experiments, PR was capable of reducing not only the high Pb2+ level, but also low concentration and it could be kept effective before contact time was 4,200 min at pH = 5. In addition, an interesting finding was that PR could reduce the mobility of Pb in the soil media. The above shows that PR has significant potential in Pb2+ removal from real wastewater.