The technology of alkaline phosphoric fertilizer on the basis of various industrial waste

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Кazan National Research Technological University

The technology of alkaline phosphoric fertilizer on the basis of various industrial wastes

Khuziakhmetov R.Кh.,

PhD in Chemistry, Associate Professor,

Khuziakhmetova A.R., assistant

Abstract

The results of experiments on the processing of low-grade Vyatka-Kama phosphate (VKP) for alkaline phosphoric fertilizer using different industrial wastes are presented in this paper. It was found that it was available to get the thermal phosphate (TP) with the content of 15-18% of the digestible P₂O₅[P₂О_5(dig)] on the basis of sulfate-soda mixture - SSM (waste alumina production) and organic sludge (waste of some of the industries of petrochemical synthesis).

Keywords: phosphate, sulfate-soda mixture, sludge, sludge recycling product (SRP), thermal phosphate.

Хузиахметов Р.Х., Хузиахметова А.Р., Технология щелочного фосфорного удобрения на основе различных промышленных отходов

Представлены результаты опытов по переработке низкокачественного Вятско-Камского фосфорита (ФВК) на щелочное фосфорное удобрение с использованием различных промышленных отходов. Установлено, что на основе сульфатно-содовой смеси - ССС (отход глиноземного производства) и органического шлама (отход некоторых производств нефтехимического синтеза) возможно получение термофосфата (ТФ) с содержанием 15-18% усвояемого Р₂О₅ [Р₂О_5(УСВ)].

Ключевые слова: фосфорит, сульфатно-содовая смесь, шлам, продукт переработки шлама (ППШ), термофосфат.

Introduction

Despite the fact that Russia is one of the world leaders in the production of fertilizers (19,6 million tone NPK- the 4th place after China, USA, India) and cereals (116 million tons of grain), the country's agricultural sector is relatively poorly developed (low yield, high cost production). One of the reasons of low yields (in 2016 - 26,3 centner/ha) is a small quantity of fertilizers applied to the soil - 40 kg/ha (1,9 million tons NPK), because approx.80% of them are exported.

The least produced fertilizers are phosphate fertilizers - 3 million tons of P₂О₅ (N - 8,2 million tons, K₂О - 8,4 million tons). The raw material for their production is apatite's (the largest deposits of apatite are located in the United States, Brazil, Russia) and sedimentary phosphates (mainly in Morocco - about 64 billion tons). The main problems of production and application of phosphoric fertilizers are the following: monopolization of apatite deposits; continuous price increase for domestic consumers; high transport costs for the transport of concentrate to processing enterprises.

As per above, low cost low-quality phosphates of fields, which are located in agricultural regions, must be involved in the processing. Primarily it is VKP (approx. 50% of the reserves of phosphate, ~ 325 million tons P₂О₅) [1, P.169].

The most perspective possible way of processing of low-grade phosphate materials is the thermal alkaline processing method, which is suitable for processing of low quality phosphate raw material with high content of Fe₂О₃ and Al₂О₃. Special attention is paid for the option of combined thermal alkaline processing with simultaneous utilization of alkaline industrial wastes (e.g., soda-sulfate mixture of alumina production, alkaline liquid combustible organic sludge from some production of petrochemical synthesis, as well as SRP [2].

The aim of this research is to develop the methods for producing alkaline phosphorous fertilizers based on the Vyatka-Kama's phosphate by using some industrial waste-additives mentioned above (WA).

Material and methods

Vyatka-Kama's phosphate has been chosen as a phosphorus raw material due to the following main factors: low cost, ease of concentrating the ore by washing (in Р₂О₅ ore~10-18%, in the concentrate - 20-24%); the impossibility of it's processing by classic acid method (the value of М_Fe-Р = Fe₂О₃/Р₂О₅ = 0,2 at the maximum allowable value М_Fe-Р = 0,14).

Used additives-wastes predominantly contain Na₂СО₃ and Na₂SО₄ in their composition. Average composition of sulfate-soda mixture (SSM) - the waste of Bogoslavskih aluminum factory (Sverdlovsk region) - is the following: Na₂СО₃- 20%, Na₂SО₄ - 70%, Al₂O₃ - 3%; the sludge of «Nizhnekamskneftehim»: NaOH -10%, organic combustibles ~ 10%, SRP: Na₂СО₃ - 90%, others are impurities.

Experiments of the TP receiving using the different waste were conducted as per scheme shown in fig. 1, the method of thermal phosphate producing was identical to method of thermal phosphate producing using Na₂CO₃ [3].

Fig. 1 - Scheme of thermal phosphate obtaining

Input parameters were varied in the following range: temperature - 900-1100 degrees; ф =15-60 minutes; the ratio of WA:VKP = 0,2ч1,5 weight; Na₂СО₃ concentration in the SSM and SRP (and also conditional Na₂СО₃ in the sludge) - 10-98%. Output parameters in the experiments were the following: content of total phosphorus (P₂О₅) and digestible phosphorus [P₂О_5(dig)].

The optimization criteria is:

К_(dig) = (P₂О_5(dig) / P₂О₅)Ч100,%.

Results

Calculation of the mixture of raw materials composition in the studied systems («VKP-sludge», «VKP-Na₂CO₃», «VKP-SRP», «VKP-SSM») were conducted depending on the state of aggregation of additives (suspension or solid), the content of the reactants (Na₂CO₃, Na₂SO₄) in them, the excessive amounts of coal. It was found that at the usage of an initial sludge the ratio of components is:

VKP: sludge = 41% : 59% = 1 : 1,45 wt. (NaOH sludge ~11%).

Thermal phosphate obtaining in the «VKP-Na₂CO₃» («VKP-SRP») system is based on the assimilable СаNaPO₄ formation by the reaction:

Са₅F(PO₄)₃ + 2Na₂CO₃ + SiO₂ = [3СаNaPO₄ + Ca₂SiO₄ + NaF] +2СО₂.

Thermal phosphate obtaining in the «VKP-sludge» system during its disposal process (by burning «phosphate + sludge» suspension) allows obtaining a finished fertilizer in one step. The burning process of an organic part of the sludge with the formation of Na₂CO₃ and its interaction with the phosphate occurs simultaneously (SiO₂ required as part of VKP):

phosphoric fertilizer sulfate soda organic sludge

2NaOH + CO₂ = Na₂CO₃ + Н₂O, ДН_Р= - 126 кJ;

2NaOH + CO + 0,5О₂ = Na₂CO₃ + Н₂O, ДН_Р= - 410кJ;

Са₅F(PO₄)₃ + 2Na₂CO₃ + SiO₂ = [3СаNaPO₄+Ca₂SiO₄+NaF] + 2CO₂.

Thermal phosphate obtaining in the «VKP-SSM» system is distinguished by the usage of additional coal (for Na₂SO₄ rehabilitation to Na₂O):

Na₂SO₄ + 2C + 1,5O₂ = Na₂O + 2CO₂ + SO₂;

Са₅F(PO₄)₃ + 2Na₂O + SiO₂ = [3СаNaPO₄ + Ca₂SiO₄ + NaF]

The experiments' results for obtaining alkaline phosphorous fertilizers based on VPK using the above industrial wastes are presented in table. 1.

Table 1

Obtaining conditions and the composition of thermal phosphates, obtained using various waste-additives (WA)

Discussion

A method of producing thermal phosphate in the «VKP-sludge» system, despite the reduction of energy consumption is quite difficult because of the low concentration of NaOH and the necessity of evaporating large volume of water (the amount of К_(dig) does not exceed 40-50%).

In the «VKP-SRP» system with a stoichiometric ratio SRP:VKP = 0,22, the experimental degree of К_(dig)is very small (due to the occurrence of different reactions with impurities). Digestible form of P₂О_5(dig)becomes optimally acceptable (К_(dig) > 90%) only with a considerable excess of additives up to 60%.

Usage of SSM system in the experiments with the absorbent carbon (С_Аbs) under substantially identical optimal firing conditions (1100 degrees, 30 min) the fertilizer with the content of P₂О_5(dig)~ 20% has been received (as in the case of Na₂СО₃). However, when the absorbent carbon is replaced by the technical coal (С_Теch) the decrease in the content of P₂О_5(dig) ~ 16% can be observed (due to the large amount of ash in the coal ~ 10%).

Data taken by the X-ray diffraction analyses shows (fig. 2) that thermal phosphates compositions derived on basis of Na₂СO₃ and Na₂SO₄ are identical.

Fig. 2 - Diffraction pattern of initial phosphate (VKP) and thermal phosphate

Fertilizers derived by thermal method, which is based on VKP and mentioned waste, meet the requirements for simple superphosphate, in terms of P₂О_5(dig) content. [4].

Conclusion

Thus, based on the provided research the following conclusion can be made: usage of sulfate-soda mixture and product disposal of organic sludge (waste of some of the industries of petrochemical synthesis) at the optimum firing conditions provides a phosphorus fertilizer with 20-21% content of P₂О_5(dig).

Список литературы/References

1. Андреев М.В. Технология фосфорных и комплексных удобрений / М. В. Андреев, А А. Бродский, Ю.А. Забелешинский и др.; под ред. С.Д. Эвенчика и А.А. Бродского, M.:,Химия, 1987. 464 с.

2. Способ получения термофосфата / Р.Х. Хузиахметов, Н.П. Мирошкин. Заявка №2015126585 от 02.07.2015 г. Решение о выдачи патента РФ от 07.09.2016 г.

3. Хузиахметов Р.Х. Технология фосфорных и комплексных удобрений из низкокачественных фосфоритов различных месторождений / Р.Х. Хузиахметов, A.М. Губайдуллина, И.П. Бреус // Вестник Казанского технологического университета. - 2009. - Т.12, № 6. - С. 52-56.

4. ГОСТ Р 5956-78. Суперфосфат простой гранулированный. Технические условия. - Введ. 1979-0101. - М.: Изд-во стандартов, 1978. - 31 с.

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