Preparation of high-purity magnesium-ammonium-phosphate fertilizer using sea bittern and industrial waste streams

The production of fertilizer magnesium ammonium phosphate (MAP, Mg.NH₄PO₄.6H₂O), commonly known as struvite, has been investigated in this study by mixing waste effluents of different sources. Effluents form pigment preparation industry rich in ammonium carbonate and poly phosphoric acid have been used as source of nitrogen (N) and phosphorus (P), respectively, whereas sea bittern has been used as a source of Mg. The stoichiometric mole ratio of the Mg²⁺ to NH₄⁺ to PO₄^3- in the mixed reaction liquid was maintained as 1:0.5:1 and 1:1:1, and the pH value of the reaction liquid was adjusted to 8.5 using sodium hydroxide. Struvite formation has been confirmed by using FTIR and P-XRD techniques. Thermal stability and morphology of the product were characterized employing thermo-gravimetric analysis (TGA) and field emission scanning electron microscopy (FE-SEM). The method reported is easy to implement and cost-effective. The adoption of the method will not only help in waste management but also in controlling environment hazards of P and N discharge in water bodies with economic benefits. The method is particularly useful for solar works which are in vicinity of industries releasing P- and N-containing effluents. After precipitation of struvite, the left out liquor can be further recycled into the salt works for enhanced recovery of common salt.