Preparation of aluminum and iron coagulant modified with active silica extraction for the removal of Cd, As, and Pb from aqueous solution

Abstract This study exploited an environmentally hazardous industrial residue of the aluminum sulfate production process as a source of amorphous silica. Industrial waste from the alum industry was used to create poly-silicic aluminum iron sulfate coagulant (PSiAlFeS). Fourier transform infrared spectroscopy (FTIR) was used to analyze the coagulant with the best silica-to-(aluminum + iron) molar ratio. The performance of the coagulant for the removal of heavy metals from synthetic wastewater was assessed. According to the coagulation tests, PSiAlFeS with a lower Si/(Al + Fe) molar ratio performed better when it came to heavy metal coagulation, such as Cd and Pb, or metalloid, such as As. Several lab trials have been conducted to evaluate the effective removal of pollutants from water by coagulation, accompanied by adsorption onto the hydroxide species particulates formed from the hydrolysis of the PSiAlFeS. The optimal parameters for more than 99% removal of Cd, Pb, and As were a dosage of 0.06 g/l at pH 7, for the removal of 10 mg of metals per liter, at a pH range of 6–7, for a contact time of 180 min. The capacities of adsorption for cadmium, lead, and arsenic ions were 161.8, 162, and 166 mg/g, respectively. The highest adsorption rates of Cd, Pb, and As ions by PSiAlFeS were observed at pH 5.0–8.0, with an optimum around 6–7. The adsorption mechanism was determined using the common models of the Langmuir, the Freundlich, and the Temkin adsorption isotherms. The adsorption of As and Cd on the precipitated complex resulting from hydrolysis of PSiAlFeS was better fitted with pseudo-1st and 2nd order and the Freundlich and Langmuir isotherm models. While Pb was better fitted to 1st order and Langmuir models.