Elimination of Hazard Cadmium Ions from Simulated Groundwater Using Hydroxyapatite Coated Filter Cake Made of Sewage Sludge and Cement Kiln Dust

Novel sorbent named coated filter cake by hydroxyapatite (CFCHAP) that prepared from precipitation of hydroxyapatite nanoparticles on the filter cake was applied in permeable reactive barrier (PRB) technique. This barrier was tested by identification of its capability in the reclamation of simulated groundwater contaminated by cadmium ions. The filter cake is the material remaining from cement kiln dust and sewage sludge after calcium and phosphate extraction for manufacture of hydroxyapatite, respectively. Isotherm studies for CFCHAP-Cd interaction elucidated that Langmuir model is a suitable expression for representation of sorption measurements with determination coefficient (R-2) > 0.99. The highest capacity of adsorption (q(m)) of CFCHAP is 34.722 mg/g which decreased slightly to 32.610 mg/g for mixture of 90% CFCHAP and 10% filter sand. The percentages of this mixture are suitable to fulfill the PRB requirements represented by acceptable hydraulic conductivity and reactivity in the continuous tests. As a function of the time, the experiments demonstrated a positive correlation between the longevity of the packed beds with the thickness of the PRB due to saturation with metal ions. The computerized solution by COMSOL 3.5a (2008) exhibited a good ability in describing the transportation of cadmium ions compared with experimental measurements. Measurements with model predictions signified that the cadmium propagation can be slowed at lower inlet concentration and water discharge for certain point along the bed.

Automated summary

A novel sorbent called CFCHAP was prepared and tested for its effectiveness in treating groundwater contaminated by cadmium ions, showing promising results for permeable reactive barrier applications. The combination of CFCHAP and filter sand meets the requirements of PRB, with experiments aligning well with computational modeling.