Study On Optimal Use Of Mother Liquor Of Potassium Nitrate Using Direct Method

With human's developing demand for high-quality crop and the increasing resource-shortage, the use of potassium nitrate which is a green fertilizer is going up year by year. Industrial production methods of potassium nitrate are as follows:double decomposition method, ion-exchange method,nitric acid direct reaction method etc, in which the process route of direct reaction method with nitric acid and potassium nitrate is used more and more due to its lower cost of raw materials, less energy consumption, but there are still many problems in the handling of a large amount of mother liquor resulting from the reaction, there will be side effects due to its high temperature of high-temperature distillation extraction method which enhances corrosion resistance requirements of equipment;neutralization nitric acid can not be recycled,and the product yield is lower. Although the production of low-temperature extraction method is in high purity and low reaction temperature, but for its complicated process and expensive extractant, the production cost will increase.In order to reduce costs and improve market competitiveness, the mother liquor must be in further optimal use.This paper makes a number of exploratory studies, and the main contents are as follows:(1)explore how to make full use of chemical energy contained in the nitric acid and hydrochloric acid of mother liquor in direct method.There is a higher concentration of H+ contained in Mother liquor,this study first consider the use of liquor to break down low-middle-grade phosphate rock for extracting P2O5, the experimental results show that the phosphorus extraction rate is 95% or more which achieve the desired objectives.(2) recycle and make use of KCl and a small amount of potassium nitrate in mother liquor, while the most effective method is transforming potassium phosphate into a slow-release fertilizer potassium and magnesium (KMgP04), step by step neutralization used in recycling.(3)after the extraction reaction, the acidc liquid is going to two steps neutralization and in the first step reaction a magnesium alkaline substances (light-burned magnesia) is added and then nitrogen-containing compounds are added in bis and ammoniated. The determinations of two-step reaction of the sediments are slow-release fertilizer with high economic value.The solution after reaction can be used as liquid fertilizer,and at -20℃environment it does not freeze in place for more than 24h, it can also be further processed for plant nutrition-based ice melting, and it requires for further study.(4) conducted a conceptual design of the process which includes logistics estimates, process design, major equipment selection, cost-effectiveness calculations.(5)make an expanded pilot study, the results show that the process can achieve expectation requirment.This method makes full use of hydrochloric acid,nitric acid in mother liquor of the direct method, recycles the potassium salt in the mother liquor as much as possible, and the process route is feasible.(6) slow-release fertilizer is made by adding the product in optimal use of mother liquor to the other nutrients, and carried out the determination of nutrient release rate respectively in the constant temperature incubator environment and in field, good release results are obtained.