RU2818698C1 - Method of producing magnesium-ammonium phosphate from saponite sludge - Google Patents

Abstract

FIELD: chemical or physical processes.

SUBSTANCE: invention relates to production of magnesium-ammonium phosphate from saponite clay slime. Production of magnesium-ammonium phosphate involves supply of starting material into a reactor with constant stirring for mixing with hydrochloric acid, neutralization with ammonia and mixing with sodium hydrophosphate, as well as filtration. Initial raw material used is saponite finely dispersed clay powder, which is stirred at temperature of 95 to 105 °C for 15 to 20 minutes. Obtained suspension is filtered to obtain a solid phase—a precipitate of amorphous silica and a liquid phase—an acidic solution of chlorides, which is directed for neutralization with ammonia with concentration of 13 % until pH=7. Obtained pulp is filtered to obtain solid phase—iron-nickel precipitate and liquid phase—magnesium chloride solution, which at temperature of 105 to 115 °C is mixed with 1M sodium hydrophosphate, and then filtered to obtain a solid phase—magnesium-ammonium phosphate and a liquid phase—a salt solution, which is sent for purification or evaporation to obtain sodium chloride.

EFFECT: method enables to obtain magnesium-ammonium phosphate by leaching with hydrochloric acid from saponite sludge.

1 cl, 4 dwg, 1 tbl, 15 ex

Description

The invention relates to the technology of inorganic substances, in particular to methods for producing magnesium products and can be used in the chemical industry for the production of magnesium phosphate from saponite clay slurry.

There is a known method for producing magnesium oxide (RF patent No. 2078039, published 1997.04.27). The essence of the method is that the original magnesite is dissolved in nitric acid and the suspension is treated with ammonia at pH 5.8-6.0 to precipitate impurities. Next, the hydroxide sludge sediment is separated from the solution, from which magnesium hydroxide is precipitated at pH 10.0-10.5. After separating the precipitate, it is washed in such a way that the calcium content in magnesium hydroxide during this operation changes within the range of 0.03-0.25 wt.%.

The disadvantage of this method is that nitric acid as an extractant does not dissolve magnesium contained in magnesite well enough, and the resulting precipitate of impurities is itself a waste of this production.

There is a known method for complex processing of serpentinite (RF patent No. 2097322, publ. 1997.11.27), serpentinite is decomposed with sulfuric acid of an optimal concentration of 20-50%. In the first stage, a precipitate of amorphous silica, silicon dioxide and undecomposed magnetic minerals is obtained. This mixture is subjected to electromagnetic separation to isolate magnetite and chromite concentrate and pure silicon dioxide. The resulting filtrate is neutralized to pH 7-8.5, and metal hydroxides of chromium-nickel-iron composition are precipitated from it. From the remaining filtrate, magnesium carbonate is obtained by carbonization, which is converted to magnesium oxide by calcination. Sodium sulfate is obtained from the final solution by evaporation.

The disadvantage of this method is that a closed cycle for the production of magnesium oxide is not ensured; the sulfuric acid and sodium hydroxide used in the technology are irreversibly consumed and excreted in the form of sodium sulfate. Subsequent extraction of silica with caustic alkali and precipitation of silicic acid gel with hydrochloric acid and ammonium chloride increases the cost of the finished product. The release of magnesium oxide is also associated with a multi-stage process.

There is a known method for producing magnesium oxide from serpentinite in a closed cycle (USSR author's certificate No. 2011638, publ. 1994.04.30), the method for producing MgO from serpentinite is that the latter is fused with ammonium sulfate at 250-400°C. The fusion product is leached with water, after which impurities Ca, Fe, Ni, Co, Si, Ca, etc. are removed from the resulting solution of magnesium sulfate by precipitating them in the form of hydroxides by fractional neutralization. The precipitate is separated by filtration, and from the filtrate by treating it with ammonia, Mg(OH) ₂ is first precipitated at pH 10.0 - 10.5, and then magnesium carbonate is precipitated at pH 11.0 - 11.5 with ammonium carbonate. After this, both precipitates are washed from the sulfate ion and subjected to heat treatment at 750°C to obtain magnesium oxide. In this case, the solution (NH ₄ ) ₂ SO ₄ obtained at the Mg(OH) ₂ precipitation stage is evaporated, granulated and sent to the sintering stage with serpentinite, and the ammonia released at this stage is condensed and recycled to the Mg(OH) ₂ precipitation stage. The degree of Mg(OH) ₂ precipitation is 98-100%.

The disadvantage of this method is the high consumption of energy resources associated with the large mass of materials processed by the melting method: the mass of the melted material is 4-6 times greater than the mass of the processed serpentinite - the product for melting consists of both serpentinite and ammonium sulfate with a weight ratio of 1:3 to 1:5.

There is a known method for obtaining magnesium from silicon-containing waste (RF patent No. 2240369, publ. 2004.11.20), a method for obtaining magnesium from silicon-containing waste, includes grinding the waste and separating it into fractions, leaching with hydrochloric acid solution to obtain a magnesium chloride suspension, separation of solution and sediment, purification and concentration of the solution, multi-stage dehydration of the solution to produce anhydrous magnesium chloride raw material for electrolysis, electrolysis to produce magnesium, chlorine and electrolyte, conversion of chlorine to produce hydrogen chloride and sending it to the stage of preparing raw materials for electrolysis, returning the electrolyte to the stage of preparing raw materials for electrolysis. In the proposed method, the siliceous precipitate, after separating the solution, is washed from the chlorine ion and subjected to heat treatment, then mixed with a reducing agent and treated with chlorine to obtain silicon tetrachloride. Heat treatment and chlorine treatment of the siliceous sediment is carried out in a fluidized bed. Treatment of siliceous sediment with chlorine is carried out in a melt of alkali metal chlorides. Before mixing with the reducing agent, the siliceous precipitate is subjected to magnetic and electrostatic separation to obtain a silica concentrate. Pitch or petroleum coke is used as a reducing agent. Before mixing with the reducing agent, the siliceous precipitate is crushed to a particle size of less than 0.20 mm, which reduces the amount of waste generated during the production of magnesium, reduces environmental pollution, and produces a new commercial product from waste - silicon tetrachloride.

The disadvantage of the process is the large amount of unused waste, so from 1000 kg of siliceous asbestos waste, 208.4 kg of magnesium was extracted, which is ~21%, the rest of the waste is siliceous sediment containing mainly compounds of silicon, magnesium, iron, nickel, cobalt , aluminum, etc. - cannot be recycled, i.e. is sent to a solid waste storage facility, which pollutes the environment; the use of polydisperse waste in the presence of asbestos fiber leads to a deterioration in the quality of the resulting magnesium chloride solutions, which leads to a complication of the purification process of the magnesium chloride solution, because During filtration, the fabric becomes clogged with asbestos fibers.

There is a known method for producing magnesium oxide (Lebedev V.A. Sedykh V.I. Metallurgy of magnesium. Textbook Ekaterinburg: USTU-UPI, 2010. 174 p.), which is carried out in the following way: preparation of an acid-salt solution sent for leaching of serpentine, carried out in the exhaust gas purification cycle of the first and second stages of carnallite dehydration. Gas purification from dust and hydrogen chloride is carried out in wet gas cleaning apparatus using wash water as an absorbent. The resulting acid-salt solution with a HC1 concentration of 15-16% is sent for leaching. The final purification of exhaust gases from chlorine occurs by absorbing it with ferric chloride. Ferric chloride, formed as a result of the reaction, is the starting material for the production of pigments based on iron oxide. Before leaching, crushed serpentinite is subjected to classification and magnetic separation, and a magnetic fraction of serpentinite enriched in iron and nickel is used for leaching. Leaching of serpentine with an acid-salt solution is carried out in reactors at a temperature of 90-105°C. The resulting suspension is separated by filtration into an acidic solution of chlorides and a precipitate of amorphous silica. The solution is transferred to the neutralization and purification process, and the amorphous silica sediment is sent to the production of commercial products (liquid glass, silicon tetrachloride, sorbents, fillers). To neutralize hydrochloric acid and precipitate impurities from a solution of magnesium chloride, finely dispersed brucite Mg(OH) ₂ is used. The resulting pulp is separated in a settling tank, and the thickened part is filtered. The magnesium chloride solution, after concentration, is sent to the carnallite synthesis stage, and the iron-nickel precipitate, after appropriate preparation, can be sent to metallurgical production. A concentrated solution of MgCl ₂ , heated to 110-115°C, enters the reactor, in which it is mixed with granular waste electrolyte. The saturated solution enters the settling tank, in which the solution is purified from insoluble inclusions supplied with the electrolyte. The clarified solution is fed to a vacuum crystallization unit, in which carnallite crystals are formed. The cooled pulp is sent to thickening and filtration operations to produce synthetic carnallite containing 31.8% MgCl ₂ .

The disadvantage of the process is the need for the preparation of exhaust gases and the subsequent preparation of an acid-salt solution, as well as the introduction of ferric chloride to purify the exhaust gases from chlorine. The use of technically sophisticated equipment required for preliminary operations before the leaching procedure, such as classification and magnetic separation, while the magnetic fraction of serpentinite enriched in iron and nickel is used for leaching.

There is a known method for thermal enrichment of the saponite mineral and the production of magnesium compounds (Umirov F.E., Pirnazarov F.G., Umirov U.F., Temirov U.Sh. International Journal of Advanced Technology and Natural Sciences. 2022. vol.3(4 ), p. 15-18), adopted as a prototype, which is carried out in the following way, the saponite mineral is fired for 2 hours at a temperature of 600-900°C, the fired saponite mineral is treated with hydrochloric acid, then a solution of dihydrogen phosphate is added to the solution of calcium and magnesium chlorides. ammonium (NH ₄ )H ₂ PO ₄ . The resulting solution was shaken at 80°C for 20 minutes, the resulting solution was cooled under natural conditions until a white precipitate of magnesium ammonium phosphate formed.

The disadvantage of the process is the preliminary heat treatment of the saponite mineral; sintering of the saponite leads to a decrease in the specific surface area of the clay by 20%, which will significantly reduce the activation acid process at the stage of transition of calcium and magnesium chlorides into solution.

The technical result is the production of magnesium ammonium phosphate by leaching with hydrochloric acid from saponite sludge.

The technical result is achieved by using finely dispersed saponite clay powder as the starting material, which is stirred at a temperature of 95 to 105°C for 15 to 20 minutes, then the resulting suspension is filtered to obtain a solid phase - a precipitate of amorphous silica, which is sent to production liquid glass and the liquid phase - an acidic solution of chlorides, which is sent for neutralization with ammonia with a concentration of 13% until pH = 7 is reached, the resulting pulp is sent for filtration, obtaining a solid phase - iron-nickel sediment, which is sent to metallurgical production and a liquid phase - a solution of magnesium chloride , which is mixed with 1 M sodium hydrogen phosphate at a temperature of 105 to 115 ° C, and then filtered to obtain a solid phase - magnesium ammonium phosphate, which is used as an additive to cement solutions, and a liquid phase - brine, which is sent for cleaning or evaporation with producing sodium chloride.

The method for producing magnesium ammonium phosphate from saponite sludge is illustrated by the following figures:

Fig. 1 – schematic diagram of the method for producing magnesium ammonium phosphate;

Fig. 2 – graph of the dependence of the yield of amorphous silica on the concentration of hydrochloric acid;

Fig. 3 – graph of the dependence of the yield of iron (III) hydroxide on the concentration of ammonia;

Fig. 4 – graph of the dependence of the yield of magnesium ammonium phosphate on the concentration of sodium hydrogen phosphate.

The method is carried out as follows. The initial raw material is saponite fine clay powder, initial composition, wt.%: SiO ₂ –52.3; MgO–22.12; Fe ₂ O ₃ –9.9%; Al ₂ O ₃ – 5.7; CaO – 4.6; other – 5.38.

The feedstock is loaded into the reactor (Fig. 1), where at a temperature of 95 to 105°C it is mixed with 15% hydrochloric acid in a ratio of 1:4. After adding the hydrochloric acid solution, the stirring process occurs for 15 to 20 minutes. Next, the suspension obtained as a result of leaching is separated by filtration into an acidic solution of chlorides and a precipitate of amorphous silica. The amorphous silica sediment is used for the production of liquid glass, silicon tetrachloride, sorbents, and fillers.

The acidic solution of chlorides is sent for neutralization with ammonia with a concentration of 13% in an amount of 40 to 45 ml to achieve pH = 7 into the reactor, where precipitation of iron and nickel hydroxides occurs. The resulting pulp is sent for filtration to obtain an iron-nickel precipitate, which is sent to metallurgical production and a solution of magnesium chloride. The magnesium chloride solution is sent to the reactor, where at a temperature of 105° to 115°C it is mixed with 1M sodium hydrogen phosphate in a ratio of 1:2. Then the mixing product is sent for filtration to obtain a solid phase of magnesium ammonium phosphate, which is used as an additive to cement slurries, and liquid phase of brine solution. The brine solution, after filtration, is sent for purification or evaporation to produce sodium chloride.

The method is illustrated by the following examples.

Example 1. 5 grams of saponite clay-plastic mass is treated with 20 ml of hydrochloric acid 5% wt. at a temperature of 90°C for 5 minutes in a reactor with constant stirring. Then, the resulting pulp is filtered into an acidic solution of chlorides and a thickened mass of amorphous silica. The results of saponite processing are presented in Table 1. The yield of amorphous silica was 62%, Fig. 2. The reaction is difficult due to the low reactivity of 1% hydrochloric acid with saponite.

Table 1 - Results for leaching of magnesium ammonium phosphate from saponite

Method No. Temperature, °C Mass ratio, wt.% Extractant concentration (HCl), % Mixing time, min Exit, % I stage of leaching 1 90 1:4 5 5 62 2 95 10 10 79 3 100 15 15 83 4 105 20 20 99 5 110 25 25 99 II stage of leaching Temperature, °C Mass ratio, wt.% Extractant concentration (NH ₄ OH), % Mixing time, min Exit, % 6 – – 3 5 51 7 5 10 59 8 10 15 69 9 13 20 87 10 15 25 85 III stage of leaching Temperature, °C Mass ratio, wt.% Extractant concentration (Na ₂ HPO ₄ ), M Mixing time, min Exit, % eleven 100 1:2 0.1 5 35 12 105 0.5 10 47 13 110 1.0 15 61 14 115 1.5 20 78 15 120 2.0 25 82

Example 2. 5 grams of saponite clay-plastic mass is treated with 20 ml of hydrochloric acid 10% wt. at a temperature of 95°C for 10 minutes in a reactor with constant stirring. Then, the resulting pulp is filtered into an acidic solution of chlorides and a thickened mass of amorphous silica. The results of saponite processing are presented in Table 1. The yield of amorphous silica was 79%, Fig. 2.

Example 3. 5 grams of saponite clay-plastic mass is treated with 20 ml of hydrochloric acid 15% wt. at a temperature of 100°C for 15 minutes in a reactor with constant stirring. Then, the resulting pulp is filtered into an acidic solution of chlorides and a thickened mass of amorphous silica. The results of saponite processing are presented in Table 1. The yield of amorphous silica was 83%, Fig. 2.

Example 4. 5 grams of saponite clay-plastic mass is treated with 20 ml of hydrochloric acid 20% wt. at a temperature of 105°C for 20 minutes in a reactor with constant stirring. Then, the resulting pulp is filtered into an acidic solution of chlorides and a thickened mass of amorphous silica. The results of saponite processing are presented in Table 1. The yield of amorphous silica was 99%, Fig. 2.

Example 5. 5 grams of saponite clay-plastic mass is treated with 20 ml of hydrochloric acid 25% wt. at a temperature of 110°C for 25 minutes in a reactor with constant stirring. Then, the resulting pulp is filtered into an acidic solution of chlorides and a thickened mass of amorphous silica. The results of processing saponite are presented in table 1. The yield of amorphous silica was 99%, Fig.2.

Example 6. The filtered pulp is treated with constant stirring for 5 minutes with 40 ml of ammonia solution of 3% wt. until pH=7 is reached in the reactor. The resulting suspension is filtered into a neutral solution of magnesium chloride and a condensed mass of iron (III) hydroxide. The dependence of the yield of iron (III) hydroxide is presented in Table 1. The yield of iron (III) hydroxide was 51%, Fig. 3.

Example 7. The filtered pulp is treated with constant stirring for 10 minutes with 40 ml of ammonia solution of 5% wt. until pH=7 is reached in the reactor. The resulting suspension is filtered into a neutral solution of magnesium chloride and a condensed mass of iron (III) hydroxide. The dependence of the yield of iron (III) hydroxide is presented in table 1. The yield of iron (III) hydroxide was 59%, Fig.3.

Example 8. The filtered pulp is treated with constant stirring for 15 minutes with 40 ml of ammonia solution of 10 wt%. until pH=7 is reached in the reactor. The resulting suspension is filtered into a neutral solution of magnesium chloride and a condensed mass of iron (III) hydroxide. The dependence of the yield of iron (III) hydroxide is presented in Table 1. The yield of iron (III) hydroxide was 69%, Fig. 3.

Example 9. The filtered pulp is treated with constant stirring for 20 minutes with 40 ml of ammonia solution of 13 wt%. until pH 7 is reached in the reactor. The resulting suspension is filtered into a neutral solution of magnesium chloride and a condensed mass of iron (III) hydroxide. The dependence of the yield of iron (III) hydroxide is presented in Table 1. The yield of iron (III) hydroxide was 87%, Fig. 3.

Example 10. The filtered pulp is treated with constant stirring for 25 minutes with 40 ml of ammonia solution of 15 wt%. until pH = 7 is reached in the reactor. The resulting suspension is filtered into a neutral solution of magnesium chloride and a condensed mass of iron (III) hydroxide. The dependence of the yield of iron (III) hydroxide is presented in Table 1. The yield of iron (III) hydroxide was 85%, Fig. 3.

Example 11: 50 ml of magnesium chloride solution is mixed with 100 ml of 0.1 M sodium hydrogen phosphate in a reactor at a temperature of 100°C and stirred for 5 minutes. The resulting suspension is filtered into an alkaline solution of sodium chloride and a thickened mass of magnesium ammonium phosphate. The dependence of the yield of magnesium ammonium phosphate is presented in Table 1. The yield of magnesium ammonium phosphate was 35%, Fig. 4.

Example 12. 50 ml of magnesium chloride solution is mixed with 100 ml of 0.5 M sodium hydrogen phosphate in a reactor at a temperature of 105 ° C and stirred for 10 minutes. The resulting suspension is filtered into an alkaline solution of sodium chloride and a thickened mass of magnesium ammonium phosphate. The dependence of the yield of magnesium ammonium phosphate is presented in Table 1. The yield of magnesium ammonium phosphate was 47%, Fig. 4.

Example 13: 50 ml of magnesium chloride solution is mixed with 100 ml of 1M sodium hydrogen phosphate in a reactor at a temperature of 110°C and stirred for 15 minutes. The resulting suspension is filtered into an alkaline solution of sodium chloride and a condensed mass of magnesium ammonium phosphate. The dependence of the yield of magnesium ammonium phosphate is presented in Table 1. The yield of magnesium ammonium phosphate was 61%, Fig. 4.

Example 14: 50 ml of magnesium chloride solution is mixed with 100 ml of 1.5 M sodium hydrogen phosphate in a reactor at a temperature of 115°C and stirred for 20 minutes. The resulting suspension is filtered into an alkaline solution of sodium chloride and a thickened mass of magnesium ammonium phosphate. The dependence of the yield of magnesium ammonium phosphate is presented in Table 1. The yield of magnesium ammonium phosphate was 78%, Fig. 4.

Example 15: 50 ml of magnesium chloride solution is mixed with 100 ml of 2M sodium hydrogen phosphate in a reactor at a temperature of 120°C and stirred for 25 minutes. The resulting suspension is filtered into an alkaline solution of sodium chloride and a thickened mass of magnesium ammonium phosphate. The dependence of the yield of magnesium ammonium phosphate is presented in Table 1. The yield of magnesium ammonium phosphate was 82%, Fig. 4.

Obtaining magnesium from a saponite clay-plastic mass when treated with hydrochloric acid with a concentration of 1% at a temperature of 90 to 105°C, at a solution concentration of 3% ammonia, when treated with 0.1 M sodium hydrogen phosphate leads to incomplete dissolution of magnesium from the saponite and, as a result, to an insignificant yield of the target product, and when obtaining magnesium from saponite when treated with hydrochloric acid with a concentration of 20% at a temperature of 90-105 ° C, with a solution concentration of 15% ammonia, when treated with 2.0 M sodium hydrogen phosphate, it is not advisable due to the absence of a significant effect on the yield of the target product .

The proposed method for producing magnesium ammonium phosphate from saponite sludge using hydrochloric acid with a concentration of 15% at a temperature from 90 to 105°C for 15 minutes in a reactor with constant stirring, with the addition of an ammonia solution with a concentration of 15% and further processing with a 2M solution of sodium hydrogen phosphate will allow obtain a commercial product, magnesium ammonium phosphate, from environmental waste of a mining enterprise, achieving a yield of the target product of 90%.

Claims (1)

A method for producing magnesium ammonium phosphate from saponite sludge, including feeding the feedstock into a reactor for mixing with hydrochloric acid with constant stirring, neutralizing with ammonia and mixing with sodium hydrogen phosphate, filtration, characterized in that saponite fine clay powder is used as the feedstock, which at temperatures from 95 to 105°C, stir for 15 to 20 minutes, then the resulting suspension is filtered to obtain a solid phase - a precipitate of amorphous silica, which is sent for the production of liquid glass and a liquid phase - an acidic solution of chlorides, which is sent for neutralization with ammonia with a concentration of 13 % until pH = 7 is reached, the resulting pulp is sent for filtration to obtain a solid phase - iron-nickel sediment, which is sent to metallurgical production, and a liquid phase - a solution of magnesium chloride, which is mixed with 1 M sodium hydrogen phosphate at a temperature of 105 to 115 ° C, and then filtered to obtain a solid phase - magnesium ammonium phosphate, which is used as an additive to cement solutions, and a liquid phase - brine, which is sent for purification or evaporation to obtain sodium chloride.