V.V. Kim, S.M. Orzhanova

Scientific supervisor: doctor of chemistry M.K. Aldabergenov

Al – Farabi Kazakh National University, Almaty, Kazakhstan.

The problem of processing of low-grade Karatau phosphorites and their wastes

Chemical intensification of agriculture is, certainly, useful but, frequently, deterioration of agrotechnical soil properties, its microbiological activity, decrease in humus and disbalance of nutrients occur. This factor and the infection of the soil with different industrial wastes requires the development of new methods of obtaining effective and maximally safe fertilizers.

In the agriculture of the Republic of Kazakhstan the phosphorus fertilizers produced on the basis of the Karatau phosphorite pool are mainly used. Thephosphorites of the Chilisai deposite in Aktobe phosphorite pool are the second most important phosphorites. Despite this, the rational technology of their processing is still missing. Currently, the production of phosphorus-containing fertilizers lacks the raw materials of the acceptable quality (the amount of phosphorus (P₂O₅> 26-28%), and phosphorites containing less than 23% of P₂O₅ are classified as waste).

Traditional methods of phosphorites processing lead to the formation of the significant amounts of technogenic liquid and solid waste which contain sulfates, chlorides, nitrates, etc., and other toxic contaminants in the soluble and insoluble forms. Another problem is that widely used today high-phosphorus fertilizers, such as superphosphate, monoammonium phosphate and others, are converted to sparingly soluble, hardly available for plants, tricalcium phosphate and hydroxyapatite in the presence of alkaline neutralizing agents in the soil.

Today, the percentage of mineral phosphate fertilizers is about 25% of the world consumption of fertilizers. Over the past ten years, the global consumption of phosphate fertilizers in agriculture has increased by more than 17%, reaching 39 million tons per year. It is expected that by the end of 2015, the volume of global demand for phosphate fertilizers will reach more than 45 million tons.

The existing technologies of the production of polymeric phosphate fertilizers, usually, require:
- Modernization and innovative adaptation of the processing and preparation of raw materials;
- The development and implementation of non-waste technology;
- The application of secondary raw material in industry (low-grade phosphorites, cottrell dust, etc.).

Currently used thermal and acid-thermal processing methods of Karatau phosphorites to obtain fertilizer are accompanied by high energy expences. And if we take a look at the method of processing low-grade acid phosphate, the extraction coefficient of P₂O₅ recovery is small. Therefore, the resulting phosphoric acid is almost never applied.

We offer the most effective resource-saving technology for the processing low-grade Karatau phosphorites and cottrell milk in order to obtain polymeric phosphate fertilizers.

In laboratory research, we used the Karatau phosphorites, containing less than 21% of P2O5, as well as the variety of mechanical impurities. During the removal of phosphorites from those that are mentioned above, P₂0₅ content in the resulting phosphate was not significantly increased. The decay of the low-grade Karatau phosphates is performed with the application of the mixture of sulfuric and nitric acids, under the optimum conditions for decomposition process: the temperature is equal to 75 ° C, mixing time is 60 minutes. Further, after the completion of phosphorite decomposition, phosphorite phosphogypsum and the insoluble residue were filtered off, preliminarily, the temperature of the slurry was increased to 85 °C.

The formed phosphogypsum can be purified further. The purified phosphogypsum can be used as a binding construction material. After that, the resulting filtrate can be used for the production of polymeric mineral phosphate fertilizers containing about 40% P₂O₅. Thus, there is no complete degradation of the phosphate complex of raw materials to form the phosphates traditionally considered to be digestible (mono- and dicalcium phosphate, or other water soluble salts of phosphoric acid), but after leaching the CO₂ groups of the structure of the obtained fluorinecarbonateapatite, phosphate complex becomes more active and digestible by plants.

Another problem is that the useless accumulation of cottrell dust in the form of stored waste in the phosphoric industry of the Southern Kazakhstan.
The result of their intense use was the accumulation of a huge amount of waste, which reached tens of millions of tons by the beginning of the 2000s. Granulated waste, cottrell dust, phosphorite ore fines, sinter ifosfogips accumulated in the dumps, in total, represent a powerful threat to the ecological environment in the South.

Phosphorous, fluorine and sulfates which are the part of these wastes and dissolved in the atmospheric precipitations and infect groundwater. The fluorine content is eight times exceed the maximum acceptable concentration, reaching 8.2 milligrams per liter. For the progression of dental fluorosis, which leads to softening of the teeth and bones of humans and animals, the offspring born dead, it is enough for an organism to obtain the concentration equal to 2 milligrams. Corrosive compounds fall into the dust, causing damage to the eyes, respiratory tract, contributing to the development of cardiovascular disease, kidney damage, liver and stomach.

For instsnce, during the production of 100-120 thousand tons of yellow phosphorus per year 80-100 tons of cottrell milk containing 1% of elemental phosphorus is formed. About 1 million tonnes of cottrell milk is in slime-depositing plants. If you apply cottrell dust on the upstream stage as the recycled phosphorous raw material source of phosphorus, the main part of the problem will be solved, and the content of P₂O₅ will rise by 2 - 5%.

References:

1. Позин Технология минеральных солей. Л:Химия, 1983,ч.2.

2. Бектуров А.Б., Серазетдинов Д.З., Урих В.А. Физико-химические основы получения полифосфатных удобрений. Алма-Ата: Наука, 1979.

3. Вольфкович С.И., Марголис Ф.Г., Поляков Н.Н. ЖХП №1 11(1960).

4. Гидротермическая переработка фосфатов на удобрения и кормовые фосфаты /Вольфкович С.И., Илларионов В.В., Ионасс А.А. и др. М.;Химия, 1964.