| Phosphorus is an essential nonmetallic element,mainly existing worldwide in the form of phosphate ore.In recent years,with the extensive development of phosphate resources,high-quality phosphate resources are gradually depleted.But the dependence of the phosphate compound fertilizer industry on phosphate mineral resources is increasing daily,so the industrial production of medium and low-grade phosphate resources has become an increasingly important research direction.For this purpose,the acidolysis process characteristics of phosphate rock,which was offered by an enterprise in Zhanjiang,were first evaluated using traditional techniques in this study.And then,the acidolysis technology of the ore was investigated using the concentrated acid ore powder method.On this basis,successfully combining the process of concentrated acid hydrolysis of phosphate rock with the preparation of compound fertilizer,the process of preparation of superphosphate-based compound fertilizer and disc granulation was developed.The main research contents and results are as follow:（1）The results of phase analysis and chemical composition analysis of the phosphate ore showed that the main phase composition of the phosphate ore is fluorapatite and contains a small number of impurities,which belongs to the first grade of the classification standard of phosphate ore processed by acid method.The single factor and orthogonal experiments were carried out with the dilute acid-ore powder method.And the results showed that the most favorable conditions of the acidolysis process were as follows:the amount of acid was 100%of the theoretical amount of acid;the grinding time was 25 min,and the mass fraction of sulfuric acid was 70%.Under these conditions,the available phosphorus content,conversion rate,and free acid content of fresh superphosphate fertilizer were 12.04%,80.26%,and 13.19%,respectively.After curing for 7 days,the conversion rate increased to 93%,and the free acid decreased to 5.14%.（2）The results of single factor experiment and orthogonal experiment on the acidolysis of phosphate ore with concentrated acid-ore powder showed that when the amount of acid was 105%of the theoretical amount of acid,the grinding time was 50min,and the mass fraction of sulfuric acid was 98%,the obtained fresh calcium superphosphate fertilizer had better properties,with the available phosphorus content of 15.83%,the conversion rate of 93.79%,and the free acid content of 15.82%.After five days of curing,the conversion of available phosphorus reached 96.78%,and the free acid decreased to 9.22%.（3）Based on the acidolysis process of concentrated acid-ore powder,urea and potassium chloride were added to the system to prepare nitrogen-phosphorus fertilizer and phosphorus-potassium fertilizer.The optimum conditions for the preparation of nitrogen and phosphorus binary fertilizer were:keeping addition amount of urea to P2O5:N=1:2,and adding urea after 20 minutes of reaction.With these conditions,the phosphorus conversion rate,free acid content,nitrogen content,water content,and total nutrient content were 81.53%,10.02%,18.79%,5.75%,and 26.38%,respectively,in nitrogen and phosphorus binary fertilizer.The optimal preparation conditions of phosphorus and potassium binary fertilizer were as follows:keeping the addition amount of potassium chloride to P2O5:K2O=1:2;adding potassium chloride after 30minutes of reaction.The conversion rate of phosphorus,the content of free acid,potassium content,and total nutrient content in the product were 84.65%,9.86%,21.04%,and 29.93%,respectively.（4）Based on process of binary fertilizer preparation,diammonium hydrogen phosphate was added as the supplementary nutrient to prepare three formulations of ternary NPK compound fertilizer.The analysis results showed the total nutrients and various element nutrients in the three samples were consistent with the theoretical calculation.However,there was a large amount of water content in the three samples,and severe caking phenomenon.Due to a high content of free acid in the products prepared by the 10-8-7 and 10-10-10,it must be neutralized.（5）The disc granulation technology of the prepared compound fertilizer was studied,and the effects of different single factors on the granulation rate,particle strength,and disintegration time in water were also investigated.The results showed the optimal granulation process conditions were as follows:mass concentration of 4%calcium lignosulfonate as the binder;raw material fineness,0.180 mm;drying temperature,100℃;drying time,120 min.Under these conditions,the product granulation rate reached 85.12%,particle strength was 40.15 N,and the time of complete disintegration in water was 242 s. |
