Precipitation treatment of effluent acidic wastewater from phosphate-containing fertilizer industry: Characterization of solid and liquid products

The effluent ponds from phosphoric acid and fertilizer industries are a worldwide problem. Wastewater in these ponds contains high concentration of acids and heavy metals that seriously contaminates the environment and underground water. On the other hand, it contains valuable components such as phosphoric acid, fluorine and flousilicic acid. In this work, wastewater samples from effluent pond of the Indo Jordan Chemicals (IJC) plant were collected. These samples were characterized for their pH, and chemical composition. The pH of pond water was found to be about 0.8 due to its high content of HF, H2SiF6 and H3PO4. Potentiometric titration, chloride and fluoride ion selective electrodes and other acid base titration methods were employed to determine the content of the above acids. AAS was also used to determine the content of heavy metals in this waste water. Potentiometric titration curves were produced to determine the optimum neutralization conditions for several synthetic mixtures made from the above acids, and for real effluent wastewater. XRD, XRF and SEM analyses were employed for analysis of the products of calcium hydroxide neutralizations. It was found that fluorine is present in effluent pond water in two forms: HF and H2SiF6. Precipitation experiments revealed that the reaction of H2SiF6 with Ca(OH)2 yielded only CaF2 with no CaSiF6. Furthermore, it was found that it is possible to separate sulfate in an initial precipitation stage. Additionally, it is possible to remove almost all fluoride in the form of CaF2 leaving at least 60% of H3PO4 in water. Amorphous silica could be removed by aging the solution after fluoride removal.