Development On The Process Ofpreparing Calcium Superphosphate Andcompound Fertilizer With Low-gradephosphate Rock

As one of non-renewable resource, the content of phosphate rock has been less and less. In China,phosphaterockresource is rich in reserve but poor in grade, mainly in the middle and low grade. With the high-grade phosphate rock resources mining day after day, the production of phosphate fertilizer will have to rely on the low-grade phosphate rock resources which contain a lot of impurities.Therefore the development of the low-grade phosphate rock resources will have the vital practical significance.As the elemental manure, superphosphate(SSP) is commonly used toproduce compound fertilizer.In industry, the dry method(diluted acid-powder method) and the wet one(concentrated acid slurry method) are usually used to produce superphosphate. Combining advantages and disadvantages, a new process called concentrated acid-powder-neutralization method is developed in this study.At first, the preferential conditions and factors’ significance of concentrated acid-powder-neutralization methodwere investigated through single factor and orthogonal tests,physical property and quality of SSP were used as evaluation indexes in comparison withconcentratedacid-powder method.Designing different ratios of raw materials, concentrated acid-powder-neutralization method were used directly to prepare the superphosphate department of compound fertilizers. In the process, the preparation andpretreatment of SSP and the preparation of compound fertilizer were combined organically,different types of ternary compound fertilizerswere prepared. With cellophane of Shanxi as raw material, the concentrated acid-powder-neutralization method is improved and evaluated whether it has the applicability to this cellophane.The major results are as follows:(1) The preferential conditions of concentrated acid-powder-neutralization method:dosage of sulfuric acid is 115% of the theoretical amount, sulfuric acid concentration is 98%,dosage of ammonia is 5%, adding time of ammonia is 40 minutes.According to the analysis of range and variance, the dosage of ammonia is the most significant factor of phosphorus conversion rate, while dosage of ammonia and sulfuric acid are all significant factor of free acid content.The phosphorus conversion rate of fresh fertilizer which is prepared by concentrated acid-powder-neutralization method is 80.14% and the free acid content is 13.28%. After 7 days of curing time, the phosphorus conversion rates of matured SSP are increased to95%, and the free acid content are reduced to5%, which is able to meet the requirement of SSP products.(2) Preparation of that based on SSP: when urea is used as raw material to prepare compound fertilizer, urea should be added after mixing sulfuric acid and phosphate rock for 25 minutes, and the addition of ureashould be controlled in the equivalent of P2O5.When potassium chloride is used as the potassium source to prepare compound fertilizer, it should be added after mixing for 5 minutes. The physical property of compound fertilizer that has different ratio of phosphorus to potassium varies greatly but is dry and no-caking. With designingdifferent ratio of raw materials, compound fertilizer whichmeets requirements of nutrientcan be prepared by concentrated acid-powder-neutralization method.(3) With cellophane of Shanxi as raw material, whencompound fertilizer is prepared by concentrated acid-powder-neutralization method, dosage of sulfuric acid should beincreasedfrom 115% to 120%, and other conditions are the same, which shows that new process has applicability of this cellophane. On the basis of SSP that prepared by concentratedacid-powder-neutralization method, ternary compound fertilizer that meet requirements of nutrient can be obtained.