A method for stabilizing calcium-arsenic slag using copper tailings

Abstract

The present invention belongs to the field of treatment of arsenic-containing waste residue stabilization technology, and specifically discloses a method for stabilizing calcium arsenic residue by using copper tailings. The method comprises the following steps: obtaining calcium arsenic residue by treating arsenic-containing waste liquid through lime precipitation method, and drying the calcium arsenic residue to constant weight; ball-milling the dried calcium arsenic residue; uniformly mixing the ball-milled powder with flotation copper tailings, and then adding an acid solution and mixing and stirring; evaporating the obtained mixture until the acid solution is evaporated to dryness, thereby realizing the stabilization treatment of calcium arsenic residue. The present invention uses sulfuric acid to dissolve and release iron and silicon in the flotation tailings of copper smelting plants. During the processes of mixing and stirring and heating, As(Ⅲ) in the calcium arsenic residue and ferrous ions dissolved and released from the flotation copper tailings of copper smelting plants are oxidized by oxygen in the air to As(Ⅴ) and Fe(Ⅲ), further generating iron-containing arsenic minerals to stabilize arsenic, enhancing its stability, and further reducing the toxic leaching of arsenic.

Description

Technical Field

[0001] The present invention belongs to the technical field of arsenic-containing waste residue stabilization, and particularly relates to a method for stabilizing calcium arsenate slag by using copper tailings slag. Background Art

[0002] Arsenic is a commonly existing toxic non-metal, which is widely associated with non-ferrous metal (such as copper, lead, zinc, antimony, gold) ores. It is estimated that the non-ferrous metal industry in China discharges tens of thousands of tons of arsenic every year. Due to the high toxicity of arsenic and the limited market, most of the arsenic must be removed from arsenic-containing wastewater in the form of solid precipitation. The most common precipitation methods mainly include lime neutralization method, iron-arsenic coprecipitation method, sulfide precipitation method, scorodite precipitation method, etc. Due to its relatively low cost and simple operation, the lime neutralization method is widely used in the treatment of arsenic-containing wastewater in most metal metallurgy industries around the world. However, this process inevitably generates a large amount of calcium arsenate slag, which is a hazardous solid waste with high arsenic content and poor stability. Calcium arsenite or calcium arsenate is unstable in the environment and usually exhibits a high arsenic leaching concentration, which may lead to serious arsenic pollution in the storage area. Therefore, they must be treated safely and effectively. Nowadays, stabilization technology has been widely used as a waste treatment strategy before landfill, aiming to reduce the environmental risk of arsenic-containing solid waste. So far, a large number of studies have focused on solidifying arsenic-containing solid waste by using cheap cementitious materials such as cement, fly ash, and geopolymers. However, these methods generally have disadvantages such as too high volume increase rate and poor long-term stability. Since calcium-containing agents and iron-containing agents are widely used in the stabilization of arsenic-contaminated soil and low-arsenic tailings, in recent years, researchers have applied them to the stabilization of hazardous solid waste, especially solid waste with high arsenic content. Among them, lime, calcium hydroxide, and ferrous sulfate have become the most commonly used stabilizers due to their low cost.

[0003] Patent CN113443843B discloses a preparation method of a composite cementitious agent for detoxifying arsenic-containing waste residue. In this method, industrial waste residue, diatomite, and sodium hydroxide are prepared into a mixed solution, subjected to hydrothermal reaction, separated by solid-liquid separation, roasted, then ball-milled and sieved to obtain the composite cementitious agent. This agent can produce highly efficient specific binding with free arsenic in the arsenic-containing waste residue, generate strong physical and coordination adsorption, and form a dense coating structure in a short time to reduce the migration rate of arsenic, so as to achieve the purpose of detoxifying the arsenic-containing waste residue. However, this method has too many control conditions, and the activity of the composite gel agent is easily inhibited.

[0004] Patent CN110606512B discloses a stabilization method of calcium arsenate slag. In this method, calcium arsenate slag, water-soluble iron salt, and water are mixed, and the mixture undergoes a chemical reaction by adjusting the pH to generate calcium iron arsenate, realizing the stabilization treatment of calcium arsenate slag. However, this method requires too long time for the chemical reaction, and the As concentration in the slurry after treatment does not reach the standard limit value allowed by the state, and a deep treatment process needs to be added.

[0005] Patent CN103028587A discloses a method for solidification treatment of arsenic calcium slag or arsenic iron slag, which dries the arsenic-containing waste slag and then oxidizes and roasts it at 600-1000°C for 1-3 hours. The As concentration in the leaching solution of the arsenic-containing waste slag treated by the invention method is far lower than the national limit (5 mg / L). However, the temperature for oxidation-reduction of this technology is too high, and the energy consumption is huge, which is not conducive to the realization of the "dual carbon" goal.

[0006] Patent CN106362347A discloses a method for treating high-concentration arsenic slag. The method uses magnesium-based stabilizers, iron-based stabilizers and silica powder as stabilizers, lime to adjust the pH, and cement as a curing agent. After treatment, the arsenic leaching toxicity is less than 2.5 mg / L. However, the method requires a pH of not less than 13, and is prone to secondary pollution under strong alkaline conditions. It cannot be safely landfilled, and the treatment cycle is relatively long.

[0007] Patent CN110746168A discloses a method for solidifying arsenic-containing sludge with steel slag and silica fume cementitious materials, which comprises mixing arsenic-containing sludge, steel slag and silica fume, using sodium silicate and sodium hydroxide as alkali activators, pressing and molding, and curing the solidified blocks for more than 28 days. The method has simple process operation and low production cost, but the material parameters are too large and the curing time is too long. Summary of the invention

[0008] The existing arsenic-containing waste slag stabilization treatment technology has problems such as long treatment cycle, large volume expansion ratio, high energy consumption and easy secondary pollution to the environment. The present invention provides a method for stabilizing calcium arsenic slag using copper tailings as a multifunctional stabilizer. The iron and silicate in the copper tailings are conducive to the stabilization of arsenic in the calcium arsenic slag, and the mineral phase of arsenic in the calcium arsenic slag is re-established through evaporation and crystallization. Compared with the traditional process, the method of the present invention has cheap and easy-to-obtain raw materials, simple operation, short treatment cycle, low energy consumption and no secondary pollution to the environment. After the calcium arsenic slag is stabilized, various indicators can meet the limit requirements specified in the "Hazardous Waste Landfill Pollution Control Standard" (GB18598-2019), and can be safely landfilled.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] A method for stabilizing calcium arsenic slag by using copper tailings comprises the following steps:

[0011] (1) treating arsenic-containing waste liquid by lime precipitation to obtain calcium arsenic slag, and drying the obtained calcium arsenic slag to constant weight;

[0012] (2) taking out the calcium arsenic slag after drying in step (1) and ball milling it;

[0013] (3) Mix the powder obtained in step (2) evenly with the flotation copper tailings, and then add an acid solution and mix and stir. Among them, the liquid-solid ratio of the acid solution to the calcium arsenide slag in step (1) is 1-5 mL: 1 g, and the iron-arsenic molar ratio of the mixture obtained by evenly mixing the powder with the flotation copper tailings is 2-4: 1;

[0014] (4) Evaporate the mixture obtained in step (3) until the acid solution evaporates to dryness, that is, realize the stabilization treatment of the calcium arsenide slag.

[0015] Further, in step (1), the specific process of treating the arsenic-containing waste liquid by the lime precipitation method is as follows: Add calcium carbonate to the arsenic-containing waste liquid for reaction, adjust the pH, after reacting for a period of time, filter, and collect solid calcium sulfate; Add calcium hydroxide to the filtrate for reaction, adjust the pH, after reacting for a period of time, filter, and collect the calcium arsenide slag; The calcium carbonate adjusts the pH of the arsenic-containing waste liquid to 2-3, preferably 2-2.5, and the reaction time is 0.1-24 h, preferably 1-10 h; The calcium hydroxide adjusts the pH of the filtrate to 11-13, preferably 12-13, and the reaction time is 1-15 h, preferably 1-8 h; The arsenic-containing waste liquid is the arsenic-containing waste liquid generated in the process of non-ferrous metal smelting; The drying treatment conditions are: the oven temperature is 60-120 °C, and the heating time is 4-8 h; Preferably, the heating temperature is 60-80 °C, and the heating time is 6-8 h.

[0016] Further, the ball milling treatment conditions in step (2) are: the ball milling speed is 150-250 rpm, the ball milling time is 2-4 h, and the ball-to-material ratio is 1-3: 1; Preferably, the ball milling speed is 200-250 rpm, the ball milling time is 2-3 h, and the ball-to-material ratio is 1-2: 1; In the calcium arsenide slag obtained by ball milling, the particle size D90 ≤ 0.165 mm, 0.074 mm ≤ particle size D80 ≤ 0.165 mm, and particle size D10 < 0.074 mm.

[0017] Further, the acid solution in step (3) is sulfuric acid, and the concentration of the acid solution is 0.5-3.5 mol / L; Preferably, the concentration of the acid solution is 0.5-2 mol / L; The liquid-solid ratio of the acid solution to the calcium arsenide slag is 2-4 mL: 1 g; Preferably, the iron-arsenic molar ratio is 2-3.5: 1.

[0018] Further, the evaporation temperature in step (4) is 60-100 °C; Preferably, the evaporation temperature is 90-100 °C; The evaporation time is 0.5 h-2.5 h; Preferably, the evaporation time is 1 h-1.5 h.

[0019] The principle of stabilizing arsenic in the calcium arsenide slag of the present invention is:

[0020] In the present invention, sulfuric acid is used to dissolve and release iron and silicon in the flotation tailings of copper smelters. During the processes of mixing, stirring, and heating, As(Ⅲ) in the calcium arsenate slag and ferrous ions released by the dissolution of the flotation copper tailings of copper smelters are oxidized by oxygen in the air to As(Ⅴ) and Fe(Ⅲ), and further form iron-arsenic minerals to stabilize arsenic. Finally, a mixture including CaSO4·2H2O, Fe(H2AsO4)3, and Ca2SiO4 is obtained, enhancing its stability and further reducing the leaching toxicity of arsenic.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] (1) Using general solid waste to treat hazardous solid waste, the present invention uses the flotation tailings after flotation in copper smelters as raw materials, without adding auxiliary materials, realizing the co-treatment of copper tailings and calcium arsenate slag. Compared with other solidification technologies, the volume increase ratio of this method is small, reducing the accumulation of solid waste and achieving the purpose of environmental protection.

[0023] (2) The process flow of the present invention is simple and the cost is low. By using the low-temperature heating method for treatment, the energy consumption is effectively reduced; the treatment cycle is short, and the arsenic pollution leakage problem caused by the accumulation of calcium arsenate slag can be effectively solved.

[0024] (3) The method adopted in the present invention is to form iron-arsenic mineral crystal nuclei by low-temperature mineral phase reconstruction of arsenate substances in calcium arsenate slag and flotation copper tailings in an acidic environment. At the same time, silicate is used as an associated mineral and combines with the newly formed iron-arsenic minerals, thereby enhancing its stability and restricting its diffusion. Description of the Drawings

[0025] Figure 1 It is the basic flow chart of the calcium arsenate slag stabilization method in the present invention;

[0026] Figure 2 It is the XRD spectrum of the raw material calcium arsenate slag in Example 1 of the present invention;

[0027] Figure 3 It is the XRD spectrum of the calcium arsenate slag after treatment in Example 1 of the present invention;

[0028] Figure 4 It is the infrared spectrum of the raw material calcium arsenate slag in Example 1 of the present invention;

[0029] Figure 5 It is the infrared spectrum of the calcium arsenate slag after treatment in Example 1 of the present invention. Detailed Embodiments

[0030] Next, the applicant further describes the present invention in detail with reference to the drawings and specific embodiments. The described embodiments are only used to help understand the present invention, but the scope of protection claimed in the claims of the present invention is not limited thereto.

[0031] The flotation copper tailings used in Examples 1-3 were provided by Hubei Zhonghuaxue Dajiang Environmental Protection Technology Co., Ltd. The total iron in the flotation copper tailings was 327.21 g / kg, and the main chemical components and their contents are shown in Table 1; the calcium arsenide slag was obtained by treating arsenic-containing waste liquid by the lime precipitation method, and the main chemical components and their contents are shown in Table 2; the specific process of treating arsenic-containing waste liquid by the lime precipitation method is as follows: calcium carbonate is added to the arsenic-containing waste liquid for reaction, the pH is adjusted to 2, after reacting for 6 h, filtration is carried out, and solid calcium sulfate is collected; calcium hydroxide is added to the filtrate for reaction, the pH is adjusted to 12, after reacting for 5 h, filtration is carried out, and calcium arsenide slag is collected; the arsenic-containing waste liquid is the arsenic-containing waste liquid generated in the process of non-ferrous metal smelting.

[0032] Table 1 Main components and contents of flotation copper tailings (wt%)

[0033]

[0034] Table 2 Main components and contents of calcium arsenide slag (wt%)

[0035]

[0036] Example 1

[0037] A method for stabilizing calcium arsenide slag with copper tailings, the specific steps are as follows:

[0038] (1) Place 5 g of calcium arsenide slag in an electrothermal blast drying oven, dry it at 80 °C for 6 h until constant weight;

[0039] (2) Take out the calcium arsenide slag after drying in step (1) and carry out ball milling. The ball milling speed is 200 rpm, the ball milling time is 3 h, and the ball-to-material ratio is 2:1.

[0040] (3) Mix the calcium arsenide slag powder obtained in step (2) with flotation copper tailings evenly according to the total iron-arsenic molar ratio of 2.5:1 in the mixture, and then add 15 mL of 1.5 mol / L sulfuric acid solution, and stir to obtain a mixture;

[0041] (4) Put the mixture obtained in step (3) into a constant temperature heating magnetic stirrer, heat and stir at 100 °C for 1 h, evaporate the solution to dryness, and carry out leaching toxicity test and BCR sequential extraction method to analyze the heavy metal forms. The test results are shown in Tables 3 and 4.

[0042] Example 2

[0043] A method for stabilizing calcium arsenide slag with copper tailings, the specific steps are as follows:

[0044] (1) Place 5 g of calcium arsenide slag in an electrothermal blast drying oven, dry it at 60 °C for 8 h until constant weight;

[0045] (2) Take out the calcium-arsenic slag after drying in step (1) and ball-mill it. The ball-mill rotation speed is 250 rpm, the ball-mill time is 2 h, and the ball-to-material ratio is 2:1.

[0046] (3) Mix the calcium-arsenic slag powder obtained in step (2) with the flotation copper tailings evenly according to the total iron-arsenic molar ratio of 2:1 in the mixture, and then add 15 mL of 1.5 mol / L sulfuric acid solution, and stir to obtain a mixture;

[0047] (4) Put the mixture obtained in step (3) into a constant-temperature heating magnetic stirrer, heat and stir at 100 °C for 1 h, evaporate the solution to dryness, conduct leaching toxicity tests and analyze the heavy metal forms by the BCR sequential extraction method. The test results are shown in Tables 3 and 4.

[0048] Example 3

[0049] A method for stabilizing calcium-arsenic slag with copper tailings, the specific steps are as follows:

[0050] (1) Place 5 g of calcium-arsenic slag in an electrothermal blast drying oven and dry it at 70 °C for 7 h until it reaches constant weight;

[0051] (2) Take out the calcium-arsenic slag after drying in step (1) and ball-mill it. The ball-mill rotation speed is 250 rpm, the ball-mill time is 2 h, and the ball-to-material ratio is 2:1.

[0052] (3) Mix the calcium-arsenic slag powder obtained in step (2) with the flotation copper tailings evenly according to the total iron-arsenic molar ratio of 2:1 in the mixture, and then add 20 mL of 1.5 mol / L sulfuric acid solution, and stir to obtain a mixture;

[0053] (4) Put the mixture obtained in step (3) into a constant-temperature heating magnetic stirrer, heat and stir at 100 °C for 1 h, evaporate the solution to dryness, conduct leaching toxicity tests and analyze the heavy metal forms by the BCR sequential extraction method. The test results are shown in Tables 3 and 4.

[0054] Table 3 Leaching toxicity test of Examples 1 - 3

[0055]

[0056] Evaluate the leaching toxicity of the obtained iron-arsenic minerals (HJ / T 299 - 2007). The arsenic leaching concentration is far less than the limit value of 5 mg / L specified in the leaching toxicity evaluation. The generated iron-arsenic mineral phase has good stability and can meet the control limit values allowed for landfill in the "Pollution Control Standard for Landfill of Hazardous Wastes" (GB 18598 - 2019).

[0057] Table 4 Analysis of heavy metal forms by BCR sequential extraction method

[0058]

[0059] The BCR sequential extraction method was used to analyze the occurrence forms of arsenic in calcium-arsenic slag, evaluate the migration rate of arsenic in calcium-arsenic slag before and after treatment and its potential risk to the environment. The occurrence forms of heavy metal arsenic are divided into acid-soluble state, reducible state, oxidizable state and residual state. The weakly acid extractable state can be directly dissolved in acidic / neutral water environment and is the most harmful; the reducible state corresponds to the form of arsenic combined with metal oxides, and the oxidizable state refers to the form of organic arsenic. The reducible state and the oxidizable state will also dissolve under appropriate pH and redox environments; the residual state is the form in which arsenic exists as stable minerals, which is the most stable and not easily dissolved.

[0060] The results show that the method of low-temperature mineral phase reconstruction adopted in the present invention converts the unstable arsenic forms (including acid-soluble state, reducible state, oxidizable state) in the original calcium-arsenic slag into stable residual state forms, realizing the stabilization of calcium-arsenic slag.

Claims

1. A method for stabilizing calcium arsenic slag using copper tailings, comprising the following steps: (1) treating arsenic-containing waste liquid by lime precipitation to obtain calcium arsenic slag, and drying the obtained calcium arsenic slag to constant weight; wherein: The arsenic-containing waste liquid is arsenic-containing waste liquid generated in the process of non-ferrous metal smelting; the specific process of treating the arsenic-containing waste liquid by lime precipitation method is: adding calcium carbonate to the arsenic-containing waste liquid for reaction, adjusting the pH value to 2-3, and filtering after a period of reaction to collect solid calcium sulfate; adding calcium hydroxide to the filtrate for reaction, adjusting the pH value to 11-13, and filtering after a period of reaction to collect calcium arsenic slag; (2) taking out the calcium arsenic slag after drying in step (1) and ball milling; in the calcium arsenic slag obtained by ball milling, the particle size D90 is ≤ 0.165 mm, the particle size D80 is ≤ 0.165 mm, and the particle size D10 is < 0.074 mm; (3) the powder obtained in step (2) is mixed evenly with the flotation copper tailings, and then an acid solution is added for mixing and stirring, wherein the acid solution is sulfuric acid, and the concentration of the acid solution is 0.5-3.5 mol / L; the liquid-to-solid ratio of the acid solution to the calcium arsenic slag in step (1) is 1-5 mL: 1 g, and the iron-arsenic molar ratio of the mixture obtained by evenly mixing the powder and the copper tailings after flotation is 2-4:1; (4) evaporating the mixture obtained in step (3) until the acid solution is evaporated to dryness, thereby achieving stabilization treatment of the calcium arsenic slag; In steps (3) and (4), sulfuric acid is used to dissolve and release iron and silicon in the flotation copper tailings. During the mixing, stirring and heating process, As(III) in the calcium arsenic slag and ferrous ions released by the dissolution of the flotation copper tailings are oxidized by oxygen in the air to As(V) and Fe(III), further generating iron-arsenic minerals. The final product is a mixture of CaSO4·2H2O, Fe(H2AsO4)3 and Ca2SiO4.

2. The method according to claim 1, characterized in that: In step (1), the calcium carbonate is used to adjust the pH value of the arsenic-containing waste liquid to 2-2.5, and the reaction time is 0.1-24 h; the calcium hydroxide is used to adjust the pH value of the filtrate to 12-13, and the reaction time is 1-15 h; the drying treatment conditions are: the oven temperature is 60-120 ° C, and the heating time is 4-8 h.

3. The method according to claim 2, characterized in that In step (1), the calcium carbonate is used to adjust the pH value of the arsenic-containing waste liquid to 2-2.5, and the reaction time is 1-10 hours; the calcium hydroxide is used to adjust the pH value of the filtrate to 12-13, and the reaction time is 1-8 hours; the drying treatment conditions are: the oven temperature is 60-80°C, and the heating time is 6-8 hours.

4. The method according to claim 1, characterized in that In step (2), the ball milling conditions are: ball milling speed is 150-250 rpm, ball milling time is 2-4 h, and ball to material ratio is 1-3:

1.

5. The method according to claim 4, characterized in that In step (2), the ball milling conditions are: ball milling speed is 200-250 rpm, ball milling time is 2-3 h, and ball to material ratio is 1-2:

1.

6. The method according to claim 1, characterized in that In step (3), the concentration of the acid solution is 0.5-2 mol / L; the liquid-solid ratio of the acid solution to the calcium arsenic slag is 2-4 mL:1 g; and the molar ratio of iron to arsenic is 2-3.5:

1.

7. The method according to claim 1, characterized in that In step (4), the evaporation temperature is 60-100°C; and the evaporation time is 0.5 h-2.5 h.

8. The method according to claim 7, characterized in that In step (4), the evaporation temperature is 90-100°C; and the evaporation time is 1 h-1.5 h.

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