Basic Research On Comprehensive Utilization Of Phosphate Sludge

The phosphate ore and the products which are produced from the ore such as phosphoric acid are widely used in the fields of the agriculture, food and industry and so on. Although China’s total reserve of the phosphate rock is ranked second in the world and has rich resources and great reserves, what worries us is that more than 80%of the ore is the middle or low grade ore. The reserves of the phosphate rock in China are gradually decreasing with the development of the industry and agriculture and the exploitation of the phosphate-ore resources. Our country ought to improve and attach much more importance to the comprehensive utilization of phosphate ore resources and meet the idea of the sustainable development.The phosphoric acid sludge is the major solid waste which is produced in the wet process for the production of the phosphoric acid through decomposing phosphate ore by the sulfuric acid. It is a very good secondary resource and the major chemical components the phosphorus, calcium, iron, magnesium, aluminum and other elements, from which phosphorus and iron can be extracted and used to produce the higher added value products. It is significantly important to promote the second exploitation and utilization of phosphorus resources and the rapid development of the economy through the comprehensive utilization of the solid waste.The content of the phosphorus and iron of the phosphoric acid sludge through the chemical method is 22.07%and 15.07%, respectively. The effects of the leaching of the phosphoric acid sludge were studied though the using of the three different leaching agent such as hydrochloric, nitric and sulfuric acid. Sulfuric acid is chosen as the leaching agent in this experiment.The research showed that the the optimized process conditions of leaching the phosphoric acid sludge are that the liquid-solid ratio (mL/g) is 3:1, the mass fraction of the sulfuric acid is 28%, the stirring speed is 300r/min, the reaction time is 60min, the reaction temperature is 80℃, the amount of washing water is 40mL each time and the washing cycle is 3.The leaching solution is used as the raw solution in the purification process, while the content of phosphorus and iron is 32.0469g/L and 21.8790g/L, respectively. After the purification and desulfurization experiment, the content of the phosphorus and iron in the purified liquid is 22.1139g/L and 16.4790g/L. The desulfurization rate of the purification process is 91.39%. The optimized process conditions of the purification desulfurization are that the leaching solution is 200mL, the stirring speed is 350r/min, the static settlement time is 80min, the reaction temperature is 60℃, the addition amount of Ca(OH)2 is 24g and the reaction time is 70min.Finally, the purified liquid is used as the raw solution to produce the phosphate-iron, in which the content of the phosphorus and iron is 22.1139g/L and 16.4790g/L, respectively. The recycling rate of the iron is 99.35%in the course of preparing phosphate-iron by adjusting the solution pH. After the production of the phosphate-iron, the content of the phosphorus is 2.6896g/L in the filtrate. Therefore, the filtrate can be used to produce the other contained phosphorus products such as the sodium phosphate, the ammonium phosphate and so on, or was circularly utilized so as to reach the comprehensive utilization ratio of the phosphorus resource. The optimized process conditions of producing the phosphate-iron are that pH is 2.0, the reaction temperature is 90℃, the stirring speed is 350r/min, the amount of washing water is 30mL each time, the washing cycle is 3 and the reaction time is 60min.