Zero residual heavy metals in aqueous media using composite coagulant converted from bauxite residue

In this study, an iron–aluminum composite (IAC) coagulant was synthesized from bauxite residue, and its applicability was investigated by harvesting biomass of Chlorella vulgaris ( C. vulgaris ). Bauxite residue is not environmentally friendly due to its high alkalinity that could pose a risk for living organisms. In this study, the conversion of the bauxite residue into IAC coagulant was done, which delivered safe utilization of bauxite residue to reduce its deteriorating impact on the environment. The prepared IAC coagulant was characterized by scanning electron microscope, Fourier transform infrared spectroscopy, and ICP-MS (inductively coupled plasma mass spectrometer). Concurrently, the applicability of the IAC was examined by harvesting the biomass of a freshwater microalgae: C. vulgaris from culture media. Several parameters (dosage, settling time, pH, biomass concentration, and age of culture) were also optimized to achieve the maximum efficiency of IAC coagulant. It was found that the 0.92 g biomass of C. vulgaris can be effectively removed from a liter of culture media by using 0.2 g of IAC in 120 min of contact time, leaving no residual metals (aluminum and iron) in aqueous media. This study showed that IAC coagulant is an efficient coagulant due to simple steps of synthesis, its high efficacy, low dose requirements, relatively short settling time, its integrity with cells, and generating no secondary pollutions.