SU823368A1 - Method of processing nitric acid phosphorite extract - Google Patents

Description

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This invention relates to a process for the processing of nitric acid extracting phosphorites of a solution resulting from the decomposition of nitric acid phosphorites, in particular, to the separation technology of calcium extract using ammonium sulfate.

A known method for treating a nitric acid extract is to isolate all or part of its content with ammonium sulphate. The latter is introduced into the extract either in the form of dry salt, or in the form of a solution, which is a waste product of caprolactam 1.

. The closest to the proposed technical essence and the achieved result is a method of processing the nitric acid extract of phosphate rock, consisting in the precipitation of 40% solution of ammonium sulfate from the calcium solution by the reaction

Ca (NH3) 2 + (NH4) 2SO4 + 2 HgO 2 + CaSq, 2 The gypsum precipitation reaction proceeds in two reactors, with ammonium sulphate being fed to the first reactor

where the nitric acid extract obtained by the decomposition of phosphate by 57% nitric acid with SO-SS C enters, the second reactor undergoes agitation of the reacted pulp, after which it is directed to filtering the rotary vacuum filter and washing the gypsum from the mother liquor 2.

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The disadvantage of this method is the low filtration rate of gypsum and, as a result, significant losses of valuable components of the drawdown - nitrogen and phosphorus C gypsum. In addition, upon receipt of ammonium sulfate by the conversion method, due to the presence of unwashed water-soluble phosphorus in the initial gypsum,

0 of the gypsum conversion process, the filterability of the chalky pulp and the yield of ammonium sulfate are reduced.

The invention of the invention is the intensification of the filtration process of gypsum and

5 reduction, loss of phosphorus and nitrogen.

This goal is achieved by assuming that the precipitation of calcium is carried out by successively feeding the nitric acid extract to the full rate.

0 agimoni sulfate solution in three

stages to pH: at the first 5-6, at the second 2-3, at the third, 9 with keeping the pulp at each stage for 15-60 minutes,

With this process, conditions are created for the formation of large uniform, well-filtered gypsum crystals, the loss of phosphorus and nitrogen with gypsum is reduced by increasing the efficiency of washing and is improved while the ammonium carbon conversion process is improved. The proposed calcium precipitation method, when gypsum precipitation starts at high pH values (the pH of the initial ammonium sulfate solution is about 9), occurs through pH 5-6, then 2-3 and the pH. 0.50, 9, a different type of gypsum crystals is formed than in the known method (in the latter, the nitric acid extract enters the system containing ammonium nitrate, excess nitric acid, determines the improved filtering properties of nitrate-phosphate7. But pulp. It should be noted that intermediate pH values of 5-fj and pH 2-3 were not chosen randomly, only when they are used, the maximum effect of the LEGATED method occurs. Use of one intermediate pH value (for example pH 5-6 or pH 2-3) with subsequent delivery of nitric acid extractpH to 0.5-0.9, impairs the process performance. Increasing the pH over 6 at a subsequent pH of 2-3 also worsens the conditions of crystal formation, obviously this is because a small amount of nitric acid is consumed from pH 9 to pH 7 zhki, amount of germ crystals

insignificantly, in this case, precipitating calcium at pH 2–3 will be determining. A similar effect occurs when the pH decreases from 2-3 to 1.25 (at a previous pH of 5-6), although the mechanism of crystal formation is different here, it is determined by the presence in the system at a pH of 1.5 significant quantities of phosphoric acid. A positive result of the proposed method is also provided in the fact that for the precipitation of precipitation there is used siu1monium sulfate containing excess ammonia, with a pH of 8.5-9.5, which is necessary to ensure a pH of 5-6 in the first stage of calcium precipitation. Ammonium sulfate, obtained by dissolving the dry salt in water, has a pH of 4, i.e., based on the foregoing, the effect of introducing nitric acid extract into such a product will be much lower.

Example. The studies were carried out in a laboratory cascade consisting of 4 serially connected reactors of 1 l each, equipped with mixing devices, dispensers: nitrate-acid extract of apatite, obtained by decomposing apatite with 56% nitric acid for 2 hours at 50 ° C (14%, nitrogen 9%, CaO 18.3%, free nitric acid 4.6%) and a 40% ammonium sulfate solution obtained by converting gypsum to carbon dioxide and ammonia (490 g / l

0 15 20 25 30 ammonium sulfate, 20 g / l ammonium carbonate, 8 g / l ammonia, pH 8.9). water baths with contact thermometers to maintain the temperature of the precipitation process between 45-50s. In all experiments, the entire amount of ammonium sulphate solution was continuously introduced into the first reactor and, depending on the experimental conditions ot, different amounts of nitric acid extract of apatite when the known method was studied - the whole extract, in other experiments up to pH values equal to 3-4, respectively 7-7.5, 5-6. The pulp flows into the second reactor, where the nitric-acid extract is fed to. The pH values are respectively 0.5-0.9, 1-1.5, 2-3, 3-4. The rest of the nitric acid extract interacts with the slurry in the third reactor to a pH of 0.5-0.9. In the fourth reactor, the reacted pulp is reacted with

1 35 same parameter. As in the previous device. The pulp flowing out of the last reactor is filtered on a Buchner funnel, the gypsum is washed with water in a three-fold countercurrent mode with a flow rate of 1 l / kg of dry gypsum. The washings are combined with the main filtrate (the solution is sent to produce fertilizers),

0 gypsum is converted by carbon dioxide and ammonia, 40% ammonium sulfate solution is returned to the precipitation of calcium from the nitric acid extract of apatite.

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The consumption of nitric acid extract is 1 l / h, the consumption of ammonium sulphate is 1 l / h.

Before conversion, washed gypsum is analyzed for water-soluble and nitrogen phosphorus content, filtration performance and moisture content of gypsum and calcium carbonate are measured. The results of the study of the precipitation of calcium from nitric acid extraction of apatite with a 40% ammonium sulfate solution are presented in the table. . .

As follows from the table, the optimal effect is achieved by introducing the nitrate-acid phosphate extraction (before applying its entire norm) to an ammonium sulfate solution successively to a pH of 5-6 and a pH of 2-3., While the productivity, filtration of gypsum is 24.6 tons / m day

loss with phosphogypsum phosphorus 0.8% nitrogen 1.1%, which in comparison with the known method makes it possible to improve the filtration performance of gypsum 3 times, to reduce the loss of nitrogen and phosphorane. 1.3%. It should be noted that in the preparation of sulphate of ammonium by the ammonium conversion of phosphoypsum, the chosen mode makes it possible (in comparison with the known method) to increase the filtering properties; chalky pulp in 2 times and reduce the loss of nitrogen (ammonia) with waste chalk on

one%. The selected mode is optimal, since a deviation from it in one direction or another leads to a deterioration of the process indicators (see the results given in the table).

5 Technical and economic advantages of the proposed method in comparison with the known method consist in intensifying the process of filtrating the nitrate-phosphate gypsum pulp and reducing the loss of phosphorus and nitrogen by increasing the efficiency of washing calcium sulphate, 1

Claims (1)

Claim 1. A method of processing nitric acid extract of phosphorites, including precipitation of calcium with ammonium sulfate, filtration of nitrate phosphate pulp, washing of gypsum with water, characterized in that, in order to intensify the process of filtration of gypsum and reduce losses of phosphorus and nitrogen, calcium precipitation is carried out by sequential supply of aero acid extract in the full norm of a solution of ammonium sulfate in three stages to pH values: on the first 5-6, on the second 2-3, on the third 0.5-0.9 with holding pulp at each stage for 15-60 minutes 40 .2. The method according to π. 1, it is important that the pH of the starting ammonium sulfate is maintained in the range of 8.5-9.5.