Method for producing basic magnesium carbonate from purified ash produced from calcium carbide

Abstract

This invention discloses a method for preparing basic magnesium carbonate from calcium carbide production purification ash, belonging to the field of solid waste resource utilization. The method mainly utilizes carbon dioxide from the lime kiln gas in calcium carbide production to pressurize and carbonize the purified ash, obtaining high-concentration heavy magnesium water. This heavy magnesium water is then catalytically degassed to obtain high-purity wet basic magnesium carbonate. Furthermore, the waste heat from the lime kiln gas in calcium carbide production is used to dry the wet basic magnesium carbonate, obtaining basic magnesium carbonate powder. This technical solution utilizes the lime kiln gas from calcium carbide production in a site-specific manner, effectively treating waste with waste, and avoiding the traditional chemical method of using chemical reagents to treat purified ash from calcium carbide production to obtain basic magnesium carbonate. Simultaneously, the catalytic degassed treatment technology significantly improves the preparation efficiency and recovery rate of basic magnesium carbonate, providing a new solution for calcium carbide production purification ash.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of solid waste resources, specifically relating to a method for preparing basic magnesium carbonate by comprehensively utilizing purified ash residue during the high-temperature calcium carbide production process in a calcium carbide furnace. Background Technology

[0002] Calcium carbide (CaC2) is an inorganic compound, typically found in industrial form as a black, lumpy solid. It is chemically reactive, reacting rapidly with water to produce acetylene (C2H2) gas and calcium hydroxide. Calcium carbide is a primary raw material for acetylene welding, organic synthesis, and the production of polyvinyl chloride (PVC). Industrially, calcium carbide is mainly produced through electric furnace smelting, reacting calcium oxide (CaO) and semi-coke at approximately 2200℃. Large-scale calcium carbide production bases have been established in Inner Mongolia, Ningxia, and Shaanxi, leveraging their abundant limestone and coal resources. Each ton of calcium carbide produced generates 2%–7% purification ash. It is estimated that over 2 million tons of purification ash are generated annually nationwide. However, testing has revealed that the main components of this purification ash are calcium oxide and magnesium oxide (MgO), with a total content approaching 80%. Furthermore, the purification ash is generally disposed of by third-party contractors at a cost, with a small portion used as a desulfurizing agent in power plants. Therefore, the resource utilization of calcium and magnesium in the purification ash residue of calcium carbide production has important environmental benefits and economic value for the sustainable development of the calcium carbide industry. Among them, magnesium, as the second largest component of purification ash from calcium carbide production, has high recycling value.

[0003] Patent (application number 202110699621.3) discloses a method and system for recovering magnesium compounds from calcium carbide furnace ash incinerators. The calcium carbide furnace ash incinerators contain 45.51 wt% CaO and 32.83 wt% MgO. Sufficient water is added to the calcium carbide furnace ash incinerators to dissolve the MgO, which is then separated and fixed. 20%–30% H₂SO₄ is added to the solid to dissolve the MgO, resulting in a MgSO₄ solution. NH₄HCO₃ is added to the MgSO₄ solution, and the mixture is stirred at 40–100°C to precipitate basic magnesium carbonate. The obtained basic magnesium carbonate is dried and calcined at temperatures above 650°C to obtain MgO.

[0004] Patent (application number 202311402925.4) discloses a method and system for preparing magnesium oxide and light calcium carbonate from calcium carbide-purified ash residue. The magnesium recovery method involves dissolving CaO from the raw material using a mixed solution of ammonium acetate and acetic acid, obtaining a magnesium-containing filter cake as the solid phase. Then, MgO in the magnesium-containing filter cake is dissolved using a mixed solution of ammonium nitrate and ammonium sulfate. After ammonia stripping, a MgSO4 solution is obtained. The MgSO4 solution then undergoes an absorption process of NH3 and CO2 to obtain a magnesium carbonate filter cake and an ammonium nitrate solution. The magnesium carbonate filter cake is then calcined to obtain MgO.

[0005] Patent (application number 201811628620.4) discloses a system and method for producing magnesium hydroxide and light calcium carbonate from purified ash residue of a calcium carbide furnace. The method for generating magnesium hydroxide includes: adding hydrochloric acid to the purified ash residue, adjusting the pH of the solution to 6 at 50°C by introducing NH3, then adding calcium hypochlorite, reacting and separating to obtain a mother liquor. NH3 is then continuously introduced into the mother liquor, and after a certain reaction time, a magnesium hydroxide filter cake is obtained.

[0006] Patent (application number 201811620503.3) discloses a method for preparing calcium sulfate and magnesium hydroxide from purified ash residue of a calcium carbide furnace. The method for recovering magnesium from the purified ash residue as magnesium hydroxide mainly involves: dissolving the purified ash residue with hydrochloric acid, separating and obtaining a mother liquor containing calcium and magnesium ions, adding the mother liquor to 40-80°C, adding ammonia water to adjust the pH to 6-7, adding an oxidant (sodium hypochlorite or calcium chlorate), adding sulfate to obtain calcium sulfate, filtering to obtain a second mother liquor, adding ammonia water to the second mother liquor to obtain magnesium hydroxide.

[0007] The above analysis shows that existing invention patents regarding the resource recovery of calcium carbide production purification ash mainly focus on separating calcium and magnesium by adding chemical acid and alkali reagents and oxidants, thereby obtaining basic magnesium carbonate and magnesium hydroxide as the main products. However, existing recovery processes are relatively complex and energy-intensive, and involve steps such as the use of ammonia and ammonia stripping, posing potential environmental safety issues. Summary of the Invention

[0008] To address the aforementioned problems, the purpose of this invention is to provide a convenient and environmentally friendly method for preparing basic magnesium carbonate from purified ash residue of calcium carbide production by utilizing byproducts from calcium carbide production in a way that is suitable for local conditions.

[0009] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for preparing basic magnesium carbonate using purified ash from calcium carbide production, comprising a lime kiln gas collection system, a calcium carbide production purified ash carbonization system, and a catalytic degassing system, the main steps of which are as follows: (1) The calcium carbide production purification ash residue is added to a certain proportion of solvent S for leaching, and solid A and mother liquor 1 are separated. Mother liquor 1 is used for subsequent recycling leaching of calcium carbide production purification ash residue.

[0010] (2) Add a certain proportion of water to the solid A obtained in (1), and then use the kiln gas of the lime kiln to perform pressurized carbonization while stirring.

[0011] (3) After carbonization, heavy magnesium water is obtained by separation.

[0012] (4) Use the residual heat of the lime kiln gas to exchange heat with the heavy magnesium water obtained in (3) so that the heavy magnesium water reaches a certain temperature, and then carry out catalytic degassing.

[0013] (5) Filter the degassed solution from (4) to obtain solid B.

[0014] (6) Use the residual heat of the lime kiln gas to heat the slurry of solid B in (5) to obtain basic magnesium carbonate.

[0015] The calcium carbide production purification ash residue is either directly collected carbonaceous ash residue or ash residue after secondary incineration.

[0016] The solvent S refers to a commonly used acid, including hydrochloric acid, sulfuric acid, and nitric acid, as well as tap water, circulating condensate, or a solution containing sodium carbonate and potassium carbonate.

[0017] The kiln gas in the lime kiln is the tail gas produced by calcining calcium carbonate in a calcium carbide plant. It contains 20% to 25% CO2 gas, is at atmospheric pressure, has a temperature of 120-200℃, and the gas flow rate of a single lime kiln is 40,000 to 60,000 Nm3 / h.

[0018] The pressurized carbonization using lime kiln gas involves passing the high-temperature tail gas generated from the calcination of calcium carbonate in a calcium carbide plant through heat exchange 1, reducing the temperature to around room temperature, and then storing it through a collection system to pressurize the mixture of solid A and mother liquor 2. The ratio of solid A to mother liquor 2 is 1:10 to 1:50.

[0019] The stirring rate is 50–300 r / min.

[0020] The pressure for pressurized carbonization using lime kiln gas is 0.1–10 MPa.

[0021] The magnesium concentration in the precipitated magnesium solution is 1–15 g / L, and the calcium concentration is 0.1–2 g / L.

[0022] The catalytic degassing refers to a catalytic method, such as microwave or ultrasonic degassing.

[0023] The slurry containing solid B, which utilizes the waste heat from the lime kiln gas, has a solid B content of 3% to 5%, a heating temperature of 90 to 100°C, and a heating time of 10 to 60 minutes.

[0024] The functions of each step in the technical method provided by this invention are as follows: (1) The main components of the purified ash residue from calcium carbide production are CaO (40~45wt%) and MgO (30~40wt%). The reaction between CaO and CO2 in the kiln gas is as follows: by controlling the pressure of CO2, a high concentration of Mg(HCO3)2 solution can be obtained, thereby improving the recovery rate of magnesium.

[0025] CaO + H2O → Ca(OH)2 Ca(OH)2 + CO2 → CaCO3 + H2O, CaCO3 + CO2 + H2O → Ca(HCO3)2, MgO + H2O → Mg(OH)2 Mg(OH)2 + CO2 → MgCO3 + H2O, MgCO3 + CO2 + H2O → Mg(HCO3)2, (2) The main component of magnesium hydroxide is Mg(HCO3)2. The bicarbonate ions are unstable and will decompose to produce CO2. Under external action such as microwave and ultrasound, CO2 is removed to generate magnesium salt precipitate (xMgCO3·yH2O), which is then transformed into basic magnesium carbonate (mMgCO3·nMg(OH)2·zH2O) under high temperature.

[0026] The beneficial effects of the method for preparing basic magnesium carbonate from purified ash residue in calcium carbide production provided by this invention are as follows: As mentioned earlier, current patents concerning the resource utilization of purified ash from calcium carbide production mainly focus on using chemical reagents to obtain calcium and magnesium salts. This approach suffers from high reagent consumption, complex processes, and potential environmental pollution problems, while neglecting the utilization of carbon dioxide and residual heat from the lime kiln gas in calcium carbide plants. Furthermore, currently published patents on the production of basic magnesium carbonate from magnesium hydroxide employ microbubbles (application number 202511737020.1) and vacuuming (application number 202311094417.4) to assist in the preparation of basic magnesium carbonate. However, these methods suffer from inconvenience or excessive time consumption, and the resulting basic magnesium carbonate particles are relatively large.

[0027] Compared to the methods in the relevant patents, the method of this invention utilizes the kiln gas and waste heat of the lime kiln in the calcium carbide plant in a way that is suitable for local conditions. This not only avoids the use of chemical reagents but also has the effect of treating waste with waste. It can quickly and efficiently obtain high-purity basic magnesium carbonate, which has strong economic value and environmental protection significance. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a simplified diagram of the method for preparing basic magnesium carbonate from purified ash residue in calcium carbide production according to the present invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. The described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 A method for preparing basic magnesium carbonate using purified ash residue from calcium carbide production mainly includes the following steps: (1) The ash residue from calcium carbide production purification, by mass fraction: 32% Ca, 19% Mg, 4% Si, 1% Fe, 0.5% Mn, and 1% S.

[0032] (2) Treat the calcium carbide production purification ash residue: mechanically crush the calcium carbide production purification ash residue after incineration (carbon-containing calcium carbide production purification ash residue does not need to be treated) to a particle size of not less than 200 mesh.

[0033] (3) The powdered calcium carbide production purification ash residue was leached with desalinated water at a liquid-to-solid ratio of 5:1. After leaching for 60 min at room temperature, it was washed with desalinated water at a ratio of 1:1 until the conductivity of the washing liquid did not exceed 3 mS / cm.

[0034] (4) The lime kiln gas containing 22% CO2 and at a temperature of 140°C is brought to room temperature through a tubular heat exchanger, and then the small particles remaining in the exhaust gas are removed by a precision dust removal bag and collected into a gas storage tank through a pipeline.

[0035] (5) The purified lime kiln gas in the gas storage tank is used to pressurize the calcium carbide production purification ash residue with a solid content of 2% after washing and separation. The pressure is 0.45 MPa and the carbonization time is 2.5 h.

[0036] (6) Depressurize the carbonized mixture, separate and filter it to obtain a magnesium hydroxide aqueous solution with a Mg2+ concentration of 4.6 g / L and a Ca2+ concentration of 187 mg / L.

[0037] (7) Microwave was used to catalytically degas the magnesium hydroxide. The microwave output power was 800 W, the frequency was 2450 MHz, and the time was 3 min.

[0038] (8) Basic magnesium carbonate is obtained by heating and drying the catalytically degassed material using the tail gas of the lime kiln.

[0039] Example 2 The experimental process and steps are as described in Example 1. The catalytic degassing method uses microwave, with a microwave output power of 700 W, a frequency of 2450 MHz, and a duration of 5 min.

[0040] Example 3 The experimental process and steps were as described in Example 1, except that the catalytic degassing method was changed to ultrasound, with a power of 420 W, a temperature of 50 °C, and a time of 30 min.

[0041] Example 4 The experimental process and steps were as described in Example 1, except that the catalytic degassing method was changed to ultrasound, with a power of 350 W, a temperature of 50 °C, and a time of 45 min.

[0042] Example Experiment Results The composition of basic magnesium carbonate was calculated as a percentage by mass, and the results are shown in the table below: Table 1 Experimental Results of Examples Example MgO CaO Fe Mn yield Example 1 41.2 0.26 0.009 0.0006 99.97 Example 2 40.7 0.37 0.007 0.0006 99.92 Example 3 41.6 0.32 0.008 0.0007 98.86 Example 4 41.5 0.41 0.009 0.0006 98.64

[0043] Comparative Example 1 The experimental procedure was the same as in Example 1, except that the catalytic degassing method was changed to vacuum, with a pressure of -0.05 MPa, a temperature of 40°C, and a time of 30 min.

[0044] Comparative Example 2 The experimental procedure was the same as in Comparative Example 1, except that the catalytic degassing method was changed to vacuum, with a pressure of -0.1 MPa, a temperature of 40℃, and a time of 30 min.

[0045] Comparative Example 3 The experimental procedure was the same as in Comparative Example 1, except that the catalytic degassing method was changed to vacuum, with a pressure of -0.05 MPa, a temperature of 50℃, and a time of 30 min.

[0046] Comparative Example 4 The experimental procedure was the same as in Comparative Example 1, except that the catalytic degassing method was changed to vacuum, with a pressure of -0.05 MPa, a temperature of 40℃, and a time of 60 min.

[0047] Comparative Example 5 The experimental procedure was the same as in Comparative Example 1, except that the catalytic degassing method was changed to vacuum, with a pressure of -0.1 MPa, a temperature of 50℃, and a time of 30 min.

[0048] Comparative experiment results: The composition of basic magnesium carbonate was calculated as a percentage by mass, and the results are shown in the table below: Table 2 Comparative Experiment Results Comparative Example MgO CaO Fe Mn yield Comparative Example 1 40.2 0.36 0.008 0.002 0.56 Comparative Example 2 40.6 0.42 0.006 0.0007 0.94 Comparative Example 3 41.1 0.26 0.007 0.0005 16.24 Comparative Example 4 40.9 0.65 0.007 0.0004 3.27 Comparative Example 5 40.5 0.41 0.009 0.0006 34.51 The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A method for preparing basic magnesium carbonate using purified ash residue from calcium carbide production, characterized in that... Includes the following steps: (1) Add a certain amount of solvent S to the purified ash residue from calcium carbide production, react and separate to obtain wet material of calcium carbide production impregnated ash residue; (2) Add a certain amount of water to the wet material of calcium carbide production purification ash residue in (1), and use carbon dioxide in the kiln gas of lime kiln to pressurize and carbonize it, and obtain heavy magnesium water after separation. (3) Use the waste heat from the lime kiln gas in calcium carbide production to preheat the heavy magnesium water in (2); (4) Catalytically degas the heavy magnesium water obtained in (2) or (3), and obtain basic magnesium carbonate wet material after separation; (5) Use the waste heat from the lime kiln gas in calcium carbide production to heat the wet basic magnesium carbonate material in (4) to obtain dry basic magnesium carbonate powder.

2. The method for preparing basic magnesium carbonate using purified ash residue from calcium carbide production according to claim 1, characterized in that, The solvent S refers to a common acid including hydrochloric acid, sulfuric acid, and nitric acid, as well as tap water, circulating condensate, or a solution containing sodium carbonate and potassium carbonate.

3. The method for preparing basic magnesium carbonate using purified ash residue from calcium carbide production according to claim 1, characterized in that, A certain amount of water is added to make the liquid-solid ratio of the calcium carbide production purification ash residue 10:1 to 50:

1.

4. The method for preparing magnesium carbonate from purified ash residue produced from calcium carbide according to claim 1, characterized in that, The kiln gas in the lime kiln contains a CO2 concentration of 20%–25%, is at atmospheric pressure, has a temperature of 120–200℃, and has a kiln gas volume of 40,000–60,000 Nm³ per kiln. 3 / h.

5. A method for preparing basic magnesium carbonate from purified ash residue produced from calcium carbide, as described in claim 1, characterized in that, The pressure for the pressurized carbonization is 0.1–10 MPa.

6. A method for preparing basic magnesium carbonate from purified ash residue produced from calcium carbide, as described in claim 1, characterized in that, The Mg in the carbonized magnesium water 2+ Concentration of 1–15 g / L, Ca 2+ The concentration is 0.1–2 g / L, and the pH is 6.9–8.

0.

7. The method for preparing basic magnesium carbonate using purified ash residue from calcium carbide production according to claim 1, characterized in that, The catalytic degassing process involves using microwaves and ultrasound to degas the magnesium hydroxide solution.

8. The method for preparing basic magnesium carbonate using purified ash residue from calcium carbide production according to claim 1, characterized in that, The wet basic magnesium carbonate material is heated using kiln gas produced from calcium carbide for 1 to 5 hours, and the moisture content of the basic magnesium carbonate powder is less than 3%.

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