Fertilizer from eppawela apatite: conversion using alkali hydroxide and quartz

Abstract

The reaction of Eppawela apatite with alkali hydroxide and quartz has been investigated in an attempt t o convert this mineral into a more soluble phosphate fertilizer. For complete breakdown four moles of sodium hydroxide are required for each mole of apatite. A molar ratio of apatite : sodium hydroxide : quartz, 1 : 4 : 2 at 9 5 0 ~ ~ after four hours heating yielded a product possessing a maximum percentage of available phosphorus. Quartz may be replaced by potashfeldspar t o obtain a potash containing phosphorus fertilizer but this requires an extended heating time. Replacement of sodium hydroxide by potassium hydroxide in the process gave a product containing high citric acid soluble phosphorus and potassium. The potassium and phosphorus containing phase in the product was identified as potassium calcium phosphate, KCaP04, which is apparently isostructural with rhenanite, NaCaPO 4' Extraction of phosphates from apatite using hot aqueous alkaline solutions followed by crystallisation of the extracts yielded crystalline soluble phosphates suitable for use#as a fertilizer.