Study On The Preparation Of Macadamia Fertilizer By Activating Low-grade Phosphate Rock With Sludge Aci

Phosphorus is an essential macroelement in plant growth,and phosphate rock is the main raw material for the production of phosphate fertilizer.China’s phosphate rock reserves account for 5%of the world,the overall average grade is about 17%,and the grade of recoverable phosphate rock reserves is only 23%.In order to solve the’crisis’of phosphate rock resources,the utilization of medium and low grade phosphate rock has become one of the research hotspots in recent years.At the same time,China’s annual output of 14 million tons of wet-process phosphoric acid will produce a large amount of sludge acid difficult to use.Therefore,how to realize the resource utilization of sludge acid is also one of the hot spots in the phosphorus resource processing industry in recent years.In this paper,sludge acid and low-grade phosphate rock were used as the main raw materials to prepare citric acid-soluble phosphate fertilizer by different process routes.The process conditions for preparing citric acid-soluble phosphate were explored and optimized.The prepared citric acid-soluble phosphate fertilizer was used as the phosphorus source of the special fertilizer for Macadamia,and the nitrogen and potassium sources of the compound fertilizer and the suitable granulation process were screened out to prepare the special fertilizer for Macadamia.Finally,the fertilizer efficiency of the special fertilizer for Macadamia was investigated by pot soil culture experiment,which provided a new way for the utilization of low-grade phosphate rock and sludge acid.（1）Using sludge acid and low-grade phosphate rock as the main raw materials,the reaction temperature was controlled by water bath operation,and the appropriate process conditions were screened by comparing the content of citrate soluble phosphorus in the reaction products.The effects of raw material ratio m acid（P₂O₅）:m ore（P₂O₅）,reaction temperature,curing temperature,curing time and water dosage on citric acid soluble phosphorus in the reaction product were investigated by single factor experiment.The results showed that when the raw material ratio m acid（P₂O₅）:m ore（P₂O₅）was 0.8,the reaction temperature was 70°C,the curing temperature was 45°C,the curing time was 5d,and the water content was 40%（the percentage of low-grade phosphate rock mass）,the content of citrate-soluble phosphorus in the reaction product was 10.69%,accounting for53%of the available phosphorus content.（2）The content of citrate-soluble phosphorus prepared by direct reaction of low-grade phosphate rock and sludge acid was 10%,which only accounts for 53%of the effective phosphorus content.Therefore,the experiment of adding conversion agent to control the reaction of low-grade phosphate rock and sludge acid to increase the content and proportion of citrate-soluble phosphorus（accounting for effective phosphorus）was carried out.The effects of raw material ratio m acid（P₂O₅）:m ore（P₂O₅）,reaction temperature,curing temperature,curing time,dosage of conversion agent（magnesium oxide,calcium oxide,yellow phosphorus slag）and water content on the citric acid soluble phosphorus in the reaction product were investigated by single factor experiment.The experimental results show that the suitable process conditions are as follows:raw material ratio m acid（P₂O₅）:m ore（P₂O₅）2.1,reaction temperature 85°C,curing temperature 55°C,curing time 7d,magnesium oxide dosage 12%or calcium oxide dosage16%or yellow phosphorus slag dosage 20%（%of the mass of water-soluble phosphorus semi-finished products）,water dosage 40%（%of the mass of water-soluble phosphorus semi-finished products）.The content of citric acid-soluble phosphorus in the final reaction product was 18%-25%,accounting for 75%-89%of the effective phosphorus content.（3）The low-grade phosphate rock and sludge acid were mixed at room temperature for reaction,and the reaction products were transferred to muffle furnace for high temperature calcination to prepare high content of citrate soluble phosphorus.The effects of raw material ratio m acid（P₂O₅）:m ore（P₂O₅）,calcination temperature and calcination time on citrate soluble phosphorus in reaction products were investigated by single factor experiment and orthogonal experiment.The experimental results showed that the suitable reaction conditions were the raw material ratio m acid（P₂O₅）:m ore（P₂O₅）of 2.5,the calcination temperature of 600℃,and the calcination time of 40min.The content of citric acid soluble phosphorus in the reaction product was 32%,accounting for 88%of the available phosphorus content.（4）The citric acid soluble phosphorus prepared by different technological routes was used as the phosphorus source of compound fertilizer.Combined with nutrient formula,preparation cost and actual production environment,the suitable granulation process and nitrogen and potassium fertilizer sources were screened out.The special fertilizer for Macadamia nut was prepared by granulation,and the pot soil culture experiment of Macadamia nut seedlings was carried out to verify the effect of the special fertilizer for Macadamia nut on plant growth.The utilization rate of N,P₂O₅ and K₂O of each fertilizer was calculated,and the best special fertilizer for Macadamia nut was selected.