A solidification treatment method for reducing the amount of arsenic leaching in arsenic-containing neutralized slag

Abstract

This application relates to the technical field of neutralization slag solidification treatment, specifically to a solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralization slag, comprising the following steps: Step 1: Pre-treating the arsenic-containing neutralization slag to obtain wet-based neutralization slag; Step 2: Adding calcium hydroxide to the wet-based neutralization slag to obtain Mixture I; Step 3: Adding ferrous sulfate to Mixture I to obtain Mixture II; Step 4: Adding a chelating agent to Mixture II to obtain Mixture III; Step 5: Adding cement to Mixture III and solidifying to obtain a solidified product of the arsenic-containing neutralization slag. This method reduces the arsenic leaching rate, with the lowest arsenic leaching amount reaching 0.2307 mg / kg, far below the maximum limit set by the national standard; and the solidification treatment cost is low.

Description

Technical Field

[0001] The present application relates to the technical field of neutralization slag solidification treatment, and in particular to a solidification treatment method for reducing the amount of arsenic leaching in arsenic-containing neutralization slag. Background Art

[0002] Arsenic occurs primarily in nature as sulfides in association with gold, copper, lead, tin, zinc, nickel, and cobalt ores. Arsenic-containing neutralized slag primarily originates from tailings left over from ore mining, arsenic-containing fly ash and alkali residue from metal smelting, and sediment obtained from the treatment of arsenic-containing wastewater and waste acid. Arsenic exists in different forms in arsenic-containing waste slag from different sources. For example, during metal smelting, arsenic primarily volatilizes as oxides in arsenic-containing dust, and as sulfides or arsenates in sediment obtained from precipitation of arsenic-containing wastewater and waste acid.

[0003] Currently, there are two main methods for treating arsenic-containing waste residues: one is stabilization / solidification, which involves encapsulating the arsenic with inert materials to prevent leakage or converting it into chemically stable arsenates for storage. The other is resource utilization, recycling the arsenic and other valuable metals contained in the waste residue to achieve both harmlessness and resource utilization. Stabilization / solidification treatment results in higher arsenic leaching rates, and the added chemicals increase treatment costs. Summary of the Invention

[0004] The present invention aims to provide a solidification treatment method for reducing the arsenic leaching amount in arsenic-containing neutralized slag. After pre-treatment, calcium hydroxide, ferrous sulfate, thiourea and cement are sequentially added to the arsenic-containing neutralized slag to obtain a mixture, thereby reducing the arsenic leaching rate and solving the problems existing in the prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following solutions:

[0006] A solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag comprises the following steps:

[0007] Step 1: pre-treating the humidity of the arsenic-containing neutralized slag to obtain wet-based neutralized slag;

[0008] Step 2: adding calcium hydroxide to the wet base and slag to obtain mixture I;

[0009] Step 3: adding ferrous sulfate to mixture I to obtain mixture II;

[0010] Step 4: adding a chelating agent to mixture II to obtain mixture III;

[0011] Step 5: Add cement to mixture III, and obtain arsenic-containing neutralized slag solidified material after solidification.

[0012] In the present application, the arsenic-containing neutralized slag is first pretreated so that the humidity of the obtained wet-based neutralized slag is within a certain range. On the one hand, this ensures the effect of the chemical reactions in steps two to four; on the other hand, it ensures the morphology of the solidified body of the arsenic-containing neutralized slag. A high moisture content will result in a longer curing time in the later stage, and a low moisture content will result in poor curing effect.

[0013] Calcium hydroxide, ferrous sulfate, and a chelating agent are sequentially added to the wet neutralized slag, causing the arsenate in the slag to react to form calcium arsenate or calcium arsenite. This arsenate then reacts with the ferrous sulfate through electrostatic attraction to form an outer complex, i.e., an adsorbed coprecipitated compound. Simultaneously, free arsenic directly reacts with free iron ions through ligand exchange to form an inner complex, thereby generating a sparingly soluble iron-arsenic compound. Thiourea is used as the chelating agent, which causes the sparingly soluble iron-arsenic compound to form a relatively stable metal complex. This metal complex then reacts with cement, which primarily acts as a gelling agent to gel the relatively stable metal complex. The resulting mixture is then solidified to form an arsenic-containing neutralized slag solidified material, enhancing the solidification effect and hardness of the solidified material. Simultaneously, the solidified arsenic-containing neutralized slag is treated in a flexible landfill, maintaining the arsenic leaching rate within the range of 0.2307-1.5738 mg / kg, with a minimum arsenic leaching rate of 0.2307 mg / kg. This significantly reduces the amount of arsenic leaching from the solidified arsenic-containing neutralized slag.

[0014] Preferably, in step 1, the humidity of the wet-based neutralized slag is 30% to 60%.

[0015] Preferably, the humidity pretreatment is carried out by adding water or drying.

[0016] Before humidity pretreatment, the arsenic-containing neutralization slag can be crushed to ensure that the particle size of all neutralization slag is less than 1 mm, which is convenient for subsequent humidity pretreatment.

[0017] Preferably, in step 2, the pH of the mixture I is adjusted to 10-12;

[0018] The weight ratio of the wet-based neutralized slag to calcium hydroxide is 100:3-5.

[0019] Among them, calcium hydroxide can also form a bridging effect during the reaction here, which is helpful for the complexation and flocculation of metal ions; at the same time, calcium hydroxide plays a role in adjusting the pH range of mixture I and increasing the subsequent complexation reaction rate of wet-based neutralization slag with ferrous sulfate and thiourea.

[0020] Preferably, in step 3, the pH of mixture II is adjusted to 10-11;

[0021] The weight ratio of the wet-based neutralized slag to ferrous sulfate is 15-20:1.

[0022] Preferably, in the step 4, the weight ratio of the wet-based neutralization residue to the chelating agent is 100:0.5-0.8.

[0023] Preferably, the chelating agent is thiourea.

[0024] Among them, compounds within thiourea containing sulfur-carbon and carbon-nitrogen double bonds can all have a stabilizing effect. Within a thiourea molecule, multiple atoms have parallel P orbitals that overlap coherently, forming a single entity. P electrons move between the atoms, forming large π bonds. This increased electron activity creates a delocalization effect, which reduces the system's energy, increases stability, and evens out bond lengths. This alters the molecular configuration and properties, weakening the sulfur-carbon double bond and strengthening the carbon-nitrogen double bond. The formation of large π bonds and the donation of a pair of electrons from the sulfur atom to arsenic and mercury ions allow for the formation of relatively stable metal complexes.

[0025] Preferably, the mixing reaction time of the wet-based neutralized residue and thiourea is 15 min to 20 min.

[0026] Preferably, the weight ratio of the wet-based neutralized slag to cement is 10:1-4.

[0027] Preferably, the cement is of C325 type. The cement herein is a powdery material containing calcium carbonate, quartz, aluminate, metaaluminate, aluminum oxide, and silicate.

[0028] After the cement is added, a certain amount of water is added to the mixture formed by the cement and the mixture III to ensure that the moisture content of the mixture reaches 60% to 70% before solidification, thereby achieving a good solidification effect.

[0029] The beneficial effects of the present invention are as follows: the present invention provides a solidification treatment method for reducing the amount of arsenic leaching in arsenic-containing neutralized slag, wherein calcium hydroxide, ferrous sulfate, thiourea and cement are sequentially added to the arsenic-containing neutralized slag after pretreatment to obtain a mixture, thereby reducing the arsenic leaching rate. The minimum arsenic leaching amount is 0.2307 mg / kg, which is far lower than the maximum limit value in the national standard.

[0030] The arsenic-containing neutralized slag solidified material after solidification treatment can be disposed of in a flexible landfill without the need for rigid landfill, thereby reducing treatment costs and avoiding the cost and risk of secondary excavation disposal.

[0031] The calcium hydroxide, ferrous sulfate and thiourea adopted in the present invention reduce the actual management difficulty and the purchase cost of the medicine. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a process flow chart of a solidification treatment method for reducing the amount of arsenic leaching in arsenic-containing neutralized slag. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] Raw materials for this example: arsenic-containing neutralized slag, calcium hydroxide, ferrous sulfate, thiourea, and cement;

[0036] Arsenic-containing neutralized slag: arsenic content is 0.5%~3%; pH value is 7.77~10.25; moisture content: 16.25%~31.59%; soluble salt content: 6.03%~8.92%; arsenic leaching: 10.45 mg / kg (total content 7047~26429 mg / kg); mercury leaching: 0.0044 mg / kg (total content 104.2307 mg / kg).

[0037] Reference Figure 1 , each raw material is carried out according to the following steps:

[0038] (1) Add water or dry the arsenic-containing neutralized slag to obtain wet-based neutralized slag, so that the humidity of the wet-based neutralized slag is 30%~60%;

[0039] (2) adding calcium hydroxide to the wet-base neutralized slag, stirring to obtain mixture I, and adjusting the pH of mixture I to 10-12;

[0040] The weight ratio of the wet-based neutralized slag to calcium hydroxide is 100:3-3.5;

[0041] (3) Add ferrous sulfate to mixture I, stir and react to obtain mixture II, and adjust the pH of mixture II to 10-11;

[0042] The weight ratio of the wet-based neutralized slag to ferrous sulfate is 19-20:1;

[0043] (4) Adding thiourea to the mixture II and mixing to obtain the mixture III, wherein the weight ratio of the wet neutralized residue to thiourea is 100:0.5-0.8; and the mixing reaction time is 15 min-20 min;

[0044] (5) adding cement to the mixture III, stirring evenly to obtain a total mixture, and subjecting the mixture to natural curing to complete the solidification treatment of the arsenic-containing neutralized slag;

[0045] The weight ratio of wet-base neutralized slag to cement is 10:1~2.5, and the cement used is C325 model.

[0046] (6) The total mixture after curing is tested for pH value, leached arsenic, leached mercury, and soluble salts.

[0047] Table 1 Performance data of arsenic-containing neutralized slag after solidification treatment with different weight ratios of thiourea and cement

[0048]

[0049] According to Table 1, the weight ratio of the wet-based neutralization slag to thiourea is 100:0.5~0.8. Thiourea is added in a variable manner within this range, so that the arsenic leaching amount in the arsenic-containing neutralization slag after solidification treatment is 0.3487~0.7587 mg / kg, and the mercury leaching amount is relatively low, mostly undetectable.

[0050] Example 2

[0051] Raw materials for this example: arsenic-containing neutralized slag, calcium hydroxide, ferrous sulfate, thiourea, and cement;

[0052] Arsenic-containing neutralized slag: arsenic content is 0.5%~3%; pH value is 7.77~10.25; moisture content: 16.25%~31.59%; soluble salt content: 6.03%~8.92%; arsenic leaching: 10.45 mg / kg (total content 7047~26429 mg / kg); mercury leaching: 0.0044 mg / kg (total content 104.2307 mg / kg).

[0053] Prepare the raw materials according to the following steps:

[0054] (1) Add water or dry the arsenic-containing neutralized slag to obtain wet-based neutralized slag, so that the humidity of the wet-based neutralized slag is 30%~60%;

[0055] (2) adding calcium hydroxide to the wet-base neutralized slag, stirring to obtain mixture I, and adjusting the pH of mixture I to 10-12;

[0056] The weight ratio of the wet-based neutralized slag to calcium hydroxide is 100:3-5;

[0057] (3) Add ferrous sulfate to mixture I, stir and react to obtain mixture II, and adjust the pH of mixture II to 10-11;

[0058] The weight ratio of the wet-based neutralized slag to ferrous sulfate is 15-20:1;

[0059] (4) Adding thiourea to the mixture II and mixing to obtain the mixture III, wherein the weight ratio of the wet neutralized residue to thiourea is 100:0.7-0.8; and the mixing reaction time is 15 min-20 min;

[0060] (5) adding cement to the mixture III, stirring evenly to obtain a total mixture, and subjecting the mixture to natural curing to complete the solidification treatment of the arsenic-containing neutralized slag;

[0061] The weight ratio of wet-base neutralized slag to cement is 10:1~2.5, and the cement used is C325 model.

[0062] (6) The total mixture after curing is tested for pH value, leached arsenic, leached mercury, and soluble salts.

[0063] Table 2 Performance data of arsenic-containing neutralized slag after solidification treatment with different weight ratios of calcium hydroxide and ferrous sulfate

[0064]

[0065] According to Table 2, the weight ratios of wet-based neutralized slag to calcium hydroxide and ferrous sulfate are 100:3~5 and 15~20:1, respectively. The addition amounts of calcium hydroxide and ferrous sulfate are variables. Excessive or insufficient addition of the two will cause the leaching amounts of mercury and arsenic to increase, among which the minimum value of arsenic leaching amount is 0.2307 mg / kg. At the same time, the salt content has an increasing trend.

[0066] In summary, the data results of Example 1 and Example 2 show that the addition amount of calcium hydroxide, ferrous sulfate and thiourea within this range can achieve an arsenic leaching amount of 0.2307~1.5738 mg / kg after solidification treatment, with a minimum value of 0.2307 mg / kg, which is significantly lower than the maximum limit of arsenic leaching amount of the solidified material after curing according to the "Identification of Hazardous Waste Leaching Toxicity Identification Standard" (GB5085.3-2007); the arsenic-containing neutralized slag solidified material after solidification treatment can meet the requirements of flexible landfill disposal, without the need for rigid landfill, reducing treatment costs, and avoiding the cost and risk of secondary excavation disposal.

[0067] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag, characterized in that: The following steps are involved: Step 1: pre-treating the humidity of the arsenic-containing neutralization slag to obtain a wet-based neutralization slag with a humidity of 30% to 60%; Step 2: adding calcium hydroxide to the wet-base neutralized slag to obtain a mixture I containing calcium arsenate or calcium arsenite; Step 3: adding ferrous sulfate to the mixture I to obtain a mixture II containing the co-precipitated compound and the insoluble iron-arsenic compound; Step 4: adding thiourea to mixture II to obtain mixture III containing a metal complex; Step 5: Add cement to mixture III, and obtain arsenic-containing neutralized slag solidified material after solidification.

2. A solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag according to claim 1, characterized in that: The humidity pretreatment method is adding water or drying.

3. The solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag according to claim 1, characterized in that: In the step 2, the pH of the mixture I is adjusted to 10-12; The weight ratio of the wet-based neutralized slag to calcium hydroxide is 100:3-5.

4. A solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag according to claim 1, characterized in that: In the step 3, the pH of the mixture II is adjusted to 10-11; The weight ratio of the wet-based neutralized slag to ferrous sulfate is 15-20:

1.

5. The solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag according to claim 1, characterized in that: In the step 4, the weight ratio of the wet-based neutralization residue to thiourea is 100:0.5~0.

8.

6. A solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag according to claim 5, characterized in that: The mixing reaction time of the mixture II and thiourea is 15 minutes to 20 minutes.

7. A solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag according to claim 5, characterized in that: The weight ratio of the wet-based neutralized slag to cement is 10:1-4.

8. The solidification treatment method for reducing the amount of arsenic leaching from arsenic-containing neutralized slag according to claim 5, characterized in that: The cement used is C325 type.

Images