Phosphate sludge valorization as new alternative precursor for carbonated hydroxyapatite nanostructures: synthesis and characterization

During the beneficiation stage, phosphate ore processing plants generate a huge quantity of phosphate sludge (PS), consisting of washing and flotation residues. This waste has a number of negative effects, such as limiting the availability of fertile land, altering the landscape and creating visually unattractive areas. Effective management of this waste is a major challenge for the phosphate industry. This study addresses the crucial problem of PS management by innovatively producing carbonated hydroxyapatite (HAp) nanostructures using the dissolution–precipitation method. Importantly, this method is applied for the first time to Moroccan phosphate sludge. The synthesized HAp is extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR), providing in-depth insights into its properties. The investigation focuses on the impact of pH variation on crystallinity, morphology and thermal stability both with and without heat treatment at 900 °C. PLS analysis and Minitab software were used to optimize calcination temperature and pH conditions. About this analysis, ideal condition was pH = 11 and a temperature of 900 °C to synthesis optimal HAp with a crystallinity (Xc%) of 71.06% and a crystal size (Xs, nm) of 46.9. However, FTIR spectra revealed that all obtained pigments were of B type carbonated hydroxyapatites. According to SEM–EDS analysis, the as-prepared HAp nanostructure was found to be pure carbonated and similar in chemical composition to human bone with trace elements such as Na⁺, Mg²⁺, Si²⁺, Al³⁺, and F⁻. Overall, the use of phosphate sludge for HAp biomaterial synthesis provides a cost-effective, environmentally friendly approach and circular economy perspective to produce a valuable nanostructure for eventual biomedical and environmental applications.