A paving stone containing arsenic-containing waste residue and a preparation method thereof

Abstract

The present invention relates to the field of paving stone technology, and in particular to a paving stone with arsenic-containing waste residue added and a preparation method thereof, comprising the following raw materials: carbide slag, desulfurized gypsum, mineral powder, core-shell waste residue particles, fine aggregate and water; the core-shell waste residue particles sequentially include a waste residue inner core layer and a barrier wrapping layer from the inside to the outside; the waste residue inner core layer includes the following raw materials: magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water; calculated by weight, the barrier wrapping layer includes the following raw materials: 45-50 parts of slag powder, 35-42 parts of mineral powder, 7-8 parts of sodium silicate and 5-6 parts of water. The paving stone with arsenic-containing waste residue added proposed by the present invention applies arsenic-containing waste residue to the paving stone, and under the premise of reducing production costs, it not only has excellent and lasting extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stone, so as to overcome the shortcomings in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of paving stones, and in particular to a paving stone added with arsenic-containing waste residue and a preparation method thereof. Background Art

[0002] Arsenic has attracted much attention from all walks of life due to its high toxicity and volatility. However, in the current basic smelting and chemical production process, arsenic flows with the material and is ultimately stored in various slag phases and tailings in a combined state, hindering resource utilization and safe disposal. Therefore, the stabilization and disposal of arsenic-containing waste slag is a major problem that needs to be solved in the current smelting and chemical industries.

[0003] In order to solve the above problems, traditional technologies mainly use the following technical means to treat arsenic-containing waste slag as a resource: (1) pyrometallurgical treatment, which is to obtain arsenic-containing vapor separated from other materials by oxidation roasting, reduction roasting or vacuum roasting of arsenic-containing waste slag. The arsenic-containing vapor is then subjected to secondary oxidation and dust collection to obtain As2O3. However, pyrometallurgical treatment has the disadvantages of serious environmental pollution, large investment and a small range of raw material adaptability; (2) Wet arsenic extraction, which is to separate arsenic from arsenic-containing waste slag in the form of arsenate by acid leaching, alkali leaching or salt leaching, and further refine it to obtain arsenic trioxide. The wet arsenic extraction process has low energy consumption, less pollution and high efficiency, but the process is complex and the processing cost is very high. However, although the above resource recovery methods have alleviated the pollution and harm of arsenic-containing waste slag to the environment to a certain extent and realized the resource utilization of arsenic-containing waste slag, they also have problems such as low recovery efficiency and relatively limited market for arsenic products.

[0004] In order to overcome the above-mentioned defects, the prior art uses a composite curing agent obtained by mixing lime, polyferric sulfate, dolomite and cement, and uses the composite curing agent to cure the arsenate in the arsenic-containing waste residue to obtain a solidified body (i.e., paving stones). However, due to the volume shrinkage of calcium silicate hydrate, one of the hydration products of cement, microcracks and pores are formed in the paving stones, resulting in poor mechanical properties of the paving stones using cement as the gel material. In addition, tricalcium aluminate, another hydration product of cement, easily reacts with water in the system to form calcium sulfonate in the presence of sulfate ions (provided by polyferric sulfate). Arsenate easily partially replaces sulfate ions in calcium sulfonate to form arsenic-type calcium sulfonate (Ca6Al2(SO4) 3-x (AsO4) x(OH)12.26H2O), and during the crystallization growth process of this arsenical ettringite, its volume will expand significantly, resulting in local stress concentration inside the paving stone. It should be noted that due to the spatio-temporal difference between the volume shrinkage of calcium silicate hydrate and the expansion of arsenical ettringite, the volume shrinkage of calcium silicate hydrate and the expansion of arsenical ettringite cannot offset each other. Since cement itself is prone to causing pores, the tensile strength of the material is relatively low, making it easy for stress to exceed the tensile strength, which also easily induces the initiation and propagation of microcracks, ultimately forming through-cracks, further reducing the mechanical properties of the paving stone. At the same time, through-cracks are likely to increase the porosity, making it easy for water and harmful substances to invade, thereby reducing the durability of the paving stone. In addition, in an acidic environment, the arsenate has a high tendency of protonation and a large lattice distortion, making arsenical ettringite prone to decomposition in an acidic environment. This not only causes the paving stone to be prone to cracking in an acidic environment, affecting the durability of the paving stone, but also easily leads to the secondary release of arsenate, resulting in an increase in the leaching toxicity of arsenic. Even if the arsenic leaching concentration of the paving stone not immersed in an acidic environment is ≤0.3 mg / L, meeting the limit requirement of 1.2 mg / L in the "Identification Standard for Leaching Toxicity of Hazardous Wastes - GB18598-2019", its arsenic leaching concentration is likely to exceed the standard under long-term immersion in an acidic environment and is difficult to meet the strict requirement of arsenic leaching concentration ≤0.3 mg / L under long-term acidic environment. In addition, due to the use of cement as a raw material, the cost of the paving stone is relatively high.

[0005] Therefore, the existing paving stones have defects such as poor mechanical properties, insufficient durability, high arsenic leaching toxicity, and relatively high cost. Summary of the Invention

[0006] The purpose of the present invention is to propose a paving stone added with arsenic-containing waste residue. By applying the arsenic-containing waste residue to the paving stone, on the premise of reducing production costs, it not only has excellent and persistent extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stone to overcome the deficiencies in the prior art.

[0007] Another purpose of the present invention is to propose a preparation method for a paving stone added with arsenic-containing waste residue. The preparation method is simple and highly operable, and it not only has excellent and persistent extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stone.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] A paving stone added with arsenic-containing waste residue, comprising the following raw materials: carbide slag, desulfurized gypsum, mineral powder, core-shell waste residue particles, fine aggregate, and water; wherein, the particle size of the core-shell waste residue particles is 7-13 mm; calculated by mass percentage, the content of calcium hydroxide in the carbide slag is ≥8%.

[0010] The core-shell waste slag particles include a waste slag core layer and a barrier wrapping layer from the inside to the outside;

[0011] The waste slag inner core layer comprises the following raw materials: magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste slag, phosphate and water; wherein the mineral components of the arsenic-containing waste slag include arsenopyrite; the mineral components of the red mud include goethite, and the chemical components of the red mud include CaO;

[0012] Calculated by weight, the barrier wrapping layer includes the following raw materials: 45-50 parts of slag powder, 35-42 parts of mineral powder, 7-8 parts of sodium silicate and 5-6 parts of water;

[0013] The chemical compositions of the slag powder in the waste slag inner core layer and the barrier wrap layer include SiO2, Al2O3 and CaO.

[0014] Furthermore, the floor paving stone comprises the following raw materials, calculated by weight: 4.5-6 parts of carbide slag, 2.5-3.5 parts of desulfurized gypsum, 20-23 parts of mineral powder, 31-34 parts of core-shell waste slag particles, 26-30 parts of fine aggregate and 7-8 parts of water;

[0015] Calculated by weight, the inner core layer of the waste slag includes the following raw materials: 8-10 parts of magnesium oxide, 15-20 parts of mineral powder, 15-20 parts of slag powder, 5-8 parts of red mud, 40-60 parts of arsenic-containing waste slag, 0.1-0.5 parts of phosphate and 7-10 parts of water.

[0016] Furthermore, the particle size of the arsenic-containing waste residue is less than 75 μm, and the specific surface area is greater than 350 m 2 / g.

[0017] Furthermore, calculated by mass percentage, the chemical compositions of the slag powder in the waste slag inner core layer and the barrier wrap layer include SiO2 40-55%, Al2O3 24-28%, Fe2O3 5-7% and CaO 5-8%, with the remainder being loss on ignition.

[0018] Furthermore, calculated by mass percentage, the chemical composition of the red mud includes Al2O3 15-20%, SiO2 5-15%, Fe2O3 30-40%, CaO 5-10% and Na2O 5-10%, with the remainder being loss on ignition.

[0019] Furthermore, the modulus of the sodium silicate is 1.2 to 1.4.

[0020] Furthermore, calculated by mass percentage, the chemical composition of the carbide slag includes Ca(OH)2 85-90%, SiO2 3-3.5%, Fe2O3 0.8-1%, Al2O3 2-2.5% and MgO 0.8-1%, and the rest is loss on ignition.

[0021] Further, the flexural strength of the paving stone is ≥ 5 MPa, the compressive strength is ≥ 48 MPa, the arsenic leaching concentration before soaking in the acetic acid buffer solution with a pH of 2.88 is ≤ 0.2 mg / L, and the arsenic leaching concentration after soaking in the acetic acid buffer solution with a pH of 2.88 for 30 days is ≤ 0.3 mg / L.

[0022] Further, the steps for preparing the paving stone added with arsenic-containing waste residue include the following:

[0023] A. Prepare core-shell waste residue particles;

[0024] Mix the formulated amounts of magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate, and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizing machine, and obtain a waste residue inner core layer after drying;

[0025] Mix the formulated amounts of slag powder, mineral powder, sodium silicate, and water evenly to obtain a barrier coating slurry;

[0026] Soak the waste residue inner core layer in the barrier coating slurry, take it out, and after steam curing and room temperature curing, form a barrier coating layer on the surface of the waste residue inner core layer to obtain core-shell waste residue particles;

[0027] B. Prepare the paving stone:

[0028] Mix the formulated amounts of carbide slag, desulfurized gypsum, mineral powder, and water evenly to obtain a gel material;

[0029] Mix the core-shell waste residue particles, fine aggregate, and gel material evenly to obtain a paving stone slurry; pour the paving stone slurry into a mold, and obtain a plate after vibration compaction; after sealing the plate and performing steam curing and room temperature curing, obtain the paving stone.

[0030] Further, in steps A and B, the curing temperature of the steam curing is 60 - 70 °C, and the curing time is 48 - 74 h; the curing time of the room temperature curing is 168 - 240 h.

[0031] The technical solution provided by the present invention may include the following beneficial effects:

[0032] 1. The mineral composition of the arsenic-containing waste residue includes arsenopyrite. In the natural environment, arsenopyrite is easily oxidized and gradually generates free and highly toxic AsO4 3- . In an aqueous environment, MgO hydrolyzes to generate Mg 2+ , and Mg 2+ can react with AsO4 3- to form magnesium arsenate precipitate, realizing the fixation of arsenic. At the same time, the mineral composition of red mud includes goethite, and the surface of goethite is rich in substances that can react with AsO43- The hydroxyl groups that form stable complexes through coordination bonds further achieve the fixation of arsenic. In addition, the hydrolysis of magnesium oxide can produce OH - to make the formulation system alkaline, and phosphate can also produce OH through the hydrolysis of phosphate - , increasing the alkalinity of the formulation system. The chemical composition of slag powder includes CaO, and the chemical composition of ore powder (generally referring to the powder obtained by crushing and processing the mined ore) itself also includes CaO, and the chemical composition of red mud also includes CaO. In an aqueous and alkaline environment, the structures of slag powder, ore powder, and red mud are damaged, thus activating the activity of CaO and releasing Ca 2+ , Ca 2 + can react with AsO4 3- to form calcium arsenate precipitate, and can also achieve the fixation of arsenic.

[0033] 2. The chemical composition of slag powder also includes SiO2 and Al2O3, and the chemical composition of ore powder itself also includes SiO2 and Al2O3. The Al2O3 in slag powder and ore powder exists in the form of an aluminum-oxygen network structure. In a strong alkaline environment, the aluminum-oxygen network structure dissociates and instantaneously generates Al 3+ , which is then surrounded by OH - and generates [Al(OH)4] - (i.e., aluminate). At the same time, in an alkaline environment, the Mg 2+ , OH - produced by the hydrolysis of magnesium oxide and the transiently generated Al 3+ react to form a positively charged lamellar structure through coprecipitation, and the positively charged lamellar structure adsorbs AsO4 3- through electrostatic interaction and / or intercalation, generating intercalated aluminum-magnesium hydrotalcite arsenate (Mg6Al2(OH) 16 (AsO4) 0.5 ·4H2O), thus achieving the fixation of arsenic.

[0034] 3. The SiO2 in slag powder and ore powder exists in the form of a silicon-oxygen network structure. In an alkaline environment, the silicon-oxygen chain in the silicon-oxygen network structure depolymerizes to generate silicate anions (including low-polymerization-degree silicate anions SiO4 4- and high-polymerization-degree silicate anions [SiO3]n 2- ). The silicate anions, the Mg 2+ produced by the hydrolysis of magnesium oxide, and OH - react to form hydrated magnesium silicate (Mg3Si2O5(OH)4). And AsO4 3- can form a coordination structure with the Mg 2+ on the surface of hydrated magnesium silicate through electrostatic interaction to achieve the adsorption and fixation of arsenic on the surface of hydrated magnesium silicate; at the same time, AsO43- can partially replace the magnesium - oxygen tetrahedron units in magnesium silicate hydrate to form Mg x-1 AsO4(Si y O 2y+1 )·nH2O intercalation structure. It can not only achieve the adsorption and fixation of arsenic inside magnesium silicate hydrate, but also release Mg in the magnesium - oxygen tetrahedron 2+ into the formulation system. And the released Mg 2+ can react with AsO4 3- in the system to form magnesium arsenate precipitate, thus further achieving the fixation of arsenic. In addition, the oxygen atoms in AsO4 3- can combine with magnesium silicate hydrate through hydrogen bonds or covalent bonds to form a composite structure, which can also fix arsenic.

[0035] 4. The barrier - wrapping layer with a relatively high density can not only wrap AsO4 3- in the inner core layer of the waste residue through chemical action to achieve the fixation of arsenic, but also prevent the leaching of AsO4 3- in the inner core layer of the waste residue by virtue of its physical barrier effect, which is beneficial to reducing the leaching toxicity of arsenic. At the same time, the barrier - wrapping layer has high acid - alkali resistance. Even in an acidic or alkaline environment, AsO4 3- in the arsenic - containing waste residue is not easily dissolved and released, which is also beneficial to reducing the leaching toxicity of arsenic. The above - mentioned multi - aspect effects make the arsenic leaching concentration of the paving stone before being soaked in the acetic acid buffer solution with a pH of 2.88 ≤ 0.2 mg / L, and the arsenic leaching concentration after being soaked in the acetic acid buffer solution with a pH of 2.88 for 30 days ≤ 0.3 mg / L, showing excellent and persistent extremely low arsenic leaching toxicity. In addition, the barrier - wrapping layer has relatively high strength, forming a hard shell layer outside the inner core layer of the waste residue, making the core - shell waste residue particles have relatively high strength, and thus enhancing the mechanical properties of the paving stone. Specific embodiments

[0036] This technical solution provides a paving stone added with arsenic - containing waste residue, including the following raw materials: carbide slag, desulfurized gypsum, ore powder, core - shell waste residue particles, fine aggregate and water; among them, the particle size of the core - shell waste residue particles is 7 - 13 mm; calculated by mass percentage, the content of calcium hydroxide in the carbide slag ≥ 8%;

[0037] The core - shell waste residue particles include an inner core layer of waste residue and a barrier - wrapping layer from the inside to the outside in sequence;

[0038] The inner core layer of the waste residue includes the following raw materials: magnesium oxide, ore powder, slag powder, red mud, arsenic - containing waste residue, phosphate and water; among them, the mineral composition of the arsenic - containing waste residue includes arsenopyrite; the mineral composition of the red mud includes goethite, and the chemical composition of the red mud includes CaO;

[0039] Calculated by mass parts, the barrier coating layer comprises the following raw materials: 45-50 parts of slag powder, 35-42 parts of ore powder, 7-8 parts of sodium silicate, and 5-6 parts of water;

[0040] The chemical compositions of the slag powder in the waste residue core layer and the barrier coating layer both include SiO2, Al2O3, and CaO.

[0041] In view of the defects in existing paving stones, such as poor mechanical properties, insufficient durability, high arsenic leaching toxicity, and high cost, this technical solution proposes a paving stone added with arsenic-containing waste residue. Through the ratio design and raw material optimization of the paving stone, the waste residue core layer, and the barrier coating layer, the arsenic-containing waste residue is applied to the paving stone. On the premise of reducing production costs, it not only has excellent and lasting extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stone to meet the actual use requirements.

[0042] Specifically, the raw materials of the waste residue core layer include magnesium oxide, ore powder, slag powder, red mud, arsenic-containing waste residue, phosphate, and water; among them, the mineral composition of the arsenic-containing waste residue includes arsenopyrite. In the natural environment, arsenopyrite is easily oxidized and gradually generates free and highly toxic AsO4 3- . In an aqueous environment, MgO hydrolyzes to generate Mg 2+ , Mg 2+ can react with AsO4 3- to form magnesium arsenate precipitation, realizing the fixation of arsenic. At the same time, the mineral composition of red mud includes goethite, and the surface of goethite is rich in hydroxyl groups that can form stable complexes with AsO4 3- through coordination bonds, further realizing the fixation of arsenic. In addition, the hydrolysis of magnesium oxide can produce OH - to make the formulation system alkaline, and phosphate can also produce OH - through the hydrolysis of phosphate groups, increasing the alkalinity of the formulation system. The chemical composition of the slag powder includes CaO, and the chemical composition of the ore powder (generally refers to the powder obtained by crushing and processing the mined ore) itself also includes CaO, and the chemical composition of red mud also includes CaO. In an aqueous and alkaline environment, the structures of the slag powder, ore powder, and red mud are destroyed, so that the activity of CaO is activated to release Ca 2+ , Ca 2+ can react with AsO4 3- to form calcium arsenate precipitation, and can also realize the fixation of arsenic.

[0043] Furthermore, in an aqueous and alkaline environment, the activation of the activity of CaO in the slag powder, ore powder, and red mud can also produce OH - , which reacts with the OH -Cooperate with each other to make the waste residue inner core layer formula system present a strong alkaline environment.

[0044] At the same time, the chemical composition of the slag powder also includes SiO2 and Al2O3, and the chemical composition of the ore powder itself also includes SiO2 and Al2O3. The Al2O3 in both the slag powder and the ore powder exists in the form of an aluminum-oxygen network structure. In a strong alkaline environment, the aluminum-oxygen network structure dissociates and instantaneously generates Al 3+ , which is then surrounded by OH - and generates [Al(OH)4] - (i.e., aluminate). At the same time, in an alkaline environment, the Mg 2+ , OH - produced by the hydrolysis of magnesium oxide and the transiently generated Al 3+ react to form a positively charged lamellar through coprecipitation, and the positively charged lamellar adsorbs AsO4 3- through electrostatic interaction and / or intercalation to generate arsenate-intercalated magnesium-aluminum hydrotalcite (Mg6Al2(OH) 16 (AsO4) 0.5 ·4H2O), thus realizing the fixation of arsenic.

[0045] In addition, the SiO2 in both the slag powder and the ore powder exists in the form of a silicon-oxygen network structure. In an alkaline environment, the silicon-oxygen chain in the silicon-oxygen network structure depolymerizes to generate silicate anions (including low-polymerization-degree silicate anions SiO4 4- and high-polymerization-degree silicate anions [SiO3]n 2- ). The silicate anions, the Mg 2+ produced by the hydrolysis of magnesium oxide, and OH - react to generate magnesium silicate hydrate (Mg3Si2O5(OH)4). And AsO4 3- can form a coordination structure with the Mg 2+ on the surface of magnesium silicate hydrate through electrostatic interaction to realize the adsorption and fixation of arsenic on the surface of magnesium silicate hydrate; at the same time, AsO4 3- can partially replace the magnesium-oxygen tetrahedron unit in magnesium silicate hydrate to form a Mg x-1 AsO4(Si y O 2y+1 )·nH2O intercalation structure, which can not only realize the adsorption and fixation of arsenic inside magnesium silicate hydrate, but also release the Mg 2+ in the magnesium-oxygen tetrahedron into the formula system, and the released Mg 2+ can react with AsO4 3- in the system to generate magnesium arsenate precipitation, thus further realizing the fixation of arsenic. In addition, the oxygen atoms in AsO4 3- can combine with magnesium silicate hydrate through hydrogen bonds or covalent bonds to form a composite structure, which can also fix arsenic.

[0046] In addition, silicate radicals with low polymerization degrees tend to react with Ca generated by CaO in slag powder and mineral powder in an alkaline environment to 2+ form calcium silicate gel. And in this system, aluminate radicals will replace some silicate radicals and enter the interior of the calcium silicate gel to form calcium aluminosilicate gel; silicate radicals with high polymerization degrees tend to react with Mg that can be hydrolyzed by MgO to 2+ generate magnesium silicate gel, and Ca generated by CaO in slag powder and mineral powder in an alkaline environment will 2+ enter the interior of the magnesium silicate gel to generate calcium magnesium silicate gel containing magnesium. That is, the final formula system forms a hybrid gel network structure of magnesium silicate gel and calcium aluminosilicate gel, and this hybrid gel network structure can form calcium magnesium silicate gel containing magnesium that wraps the arsenic waste residue, thereby realizing the fixation of arsenic.

[0047] In summary, the fixation of arsenic is achieved through the mutual cooperation of the above-mentioned various effects in the waste residue inner core layer of this technical solution.

[0048] Furthermore, the hybrid gel network structure combines the high strength of calcium aluminosilicate gel, which is beneficial to improving the strength of the waste residue inner core layer, thereby improving the strength of the paving stone; at the same time, this hybrid gel network structure can increase the compactness of the waste residue inner core layer, which is also beneficial to further improving the strength of the paving stone. In addition, the hybrid gel network structure combines the acid resistance of magnesium silicate gel, which is beneficial to improving the durability of the waste residue inner core layer, thereby improving the durability of the paving stone.

[0049] Therefore, the waste residue inner core layer is obtained by compounding magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water in this technical solution. It not only turns waste into treasure and makes full use of the arsenic-containing waste residue, but also 3- fixes AsO4 in the arsenic-containing waste residue and reduces the arsenic leaching toxicity, and is also beneficial to improving the mechanical properties and durability of the paving stone.

[0050] It should be noted that the synergistic effect among the three raw materials of mineral powder, slag powder and red mud in the waste residue inner core layer can provide sufficient calcium for the system, and the following effects will be produced: (1) Silicate radicals can react with Mg generated by the hydrolysis of MgO to 2+ generate magnesium silicate gel, and the main structure of the magnesium silicate gel is composed of magnesium octahedrons and silicon oxygen tetrahedrons, forming a layered structure similar to talc. However, the interlayer binding of pure magnesium silicate gel is weak, which easily leads to a loose structure and reduces the compressive strength and durability. And the Ca provided by mineral powder, slag powder and red mud 2+ has an ionic radius larger than that of Mg 2+ and can partially replace Mg 2+sites or are intercalated into the interlayers of magnesium silicate gel, balancing the negative charges of silicon-oxygen chains through electrostatic interactions, enhancing the interlayer connection of magnesium silicate gel, and improving the structural density; (2) Ca provided by mineral powder, slag powder, and red mud 2+ can reduce the nucleation energy barrier of magnesium silicate gel and, together with Mg 2+ , jointly promote the formation of the early gel phase and optimize the generation of the hybrid gel network structure in the inner core layer of the waste residue; (3) Ca 2+ tends to combine with silicate radicals with low polymerization degrees, while Mg 2+ is more likely to act on silicate radicals with high polymerization degrees. The synergistic effect of the two can form a more uniform gel structure, improving the mechanical properties and durability. (4) When there is no Ca 2+ in the system, Mg 2+ is prone to generating brittle magnesium hydroxide (Brucite) with OH - , damaging the continuity of calcium magnesium silicate gel. However, Ca 2+ inhibits the generation of Brucite through competitive reactions, maintaining the dominance of layered calcium magnesium silicate gel and being beneficial to maintaining the overall performance of the material. In summary, the introduction of mineral powder, slag powder, and red mud in the inner core layer of the waste residue significantly improves the strength and durability of the inner core layer of the waste residue through four mechanisms: structural strengthening, nucleation promotion, optimization of silicate radical binding, and inhibition of brittle phases.

[0051] Secondly, although the inner core layer of the waste residue can fix AsO4 3- in the arsenic-containing waste residue, thereby reducing the leaching toxicity of arsenic, its arsenic fixation ability is limited and still difficult to meet the actual use requirements. Therefore, in this technical solution, a barrier coating layer is additionally provided outside the inner core layer of the waste residue. The barrier coating layer with a higher density can not only wrap AsO4 3- in the inner core layer of the waste residue through chemical action to achieve arsenic fixation, but also prevent the leaching of AsO4 3- in the inner core layer of the waste residue by virtue of its physical barrier effect, which is beneficial to reducing the leaching toxicity of arsenic. At the same time, this barrier coating layer has high acid and alkali resistance. Even in an acidic or alkaline environment, AsO4 3- in the arsenic-containing waste residue is not easily dissolved and released, which is also beneficial to reducing the leaching toxicity of arsenic. The above-mentioned multi-faceted effects make the arsenic leaching concentration of the paving stone ≤ 0.2 mg / L before being soaked in an acetic acid buffer solution with a pH of 2.88, and the arsenic leaching concentration ≤ 0.3 mg / L after being soaked in an acetic acid buffer solution with a pH of 2.88 for 30 days, having excellent and lasting extremely low arsenic leaching toxicity. In addition, the barrier coating layer has a higher strength, forming a hard shell layer outside the inner core layer of the waste residue, making the core-shell waste residue particles have a higher strength, thereby enhancing the mechanical properties of the paving stone.

[0052] Specifically, the raw materials of the barrier coating layer include slag powder, ore powder, sodium silicate and water. When sodium silicate is added to the barrier coating layer formulation, sodium silicate undergoes a hydrolysis reaction with water to generate OH - , making the formulation system alkaline. At the same time, SiO2 in the slag powder and ore powder exists in the form of a silicon-oxygen network structure, and Al2O3 in the slag powder and ore powder exists in the form of an aluminum-oxygen network structure. In an alkaline environment, the silicon-oxygen chains in the silicon-oxygen network structure and the aluminum-oxygen chains in the aluminum-oxygen network structure are depolymerized, generating silicate and aluminate respectively. Since the addition amount of sodium silicate in the barrier coating layer formulation system is 7-8 parts, the Na + provided by sodium silicate is significantly excessive. Silicate and aluminate directly condense and polymerize in the presence of excessive Na + in the system to form sodium aluminosilicate gel (N-A-S-H) with a three-dimensional network structure. At the same time, silicate can react with Ca(OH)2, the product after the activation of the activity of CaO in the slag powder and ore powder in the system, to form calcium silicate gel mainly with a layered structure, and in this system, aluminate replaces part of the silicate and enters the interior of the calcium silicate gel to form calcium aluminosilicate gel (C-A-S-H). That is, the present formulation system finally forms a hybrid gel network structure composed of calcium aluminosilicate gel and sodium aluminosilicate gel. The hybrid gel network structure can not only wrap AsO4 3- in the waste residue inner core layer to achieve the fixation of arsenic, but also endow the barrier coating layer with high density, enabling the barrier coating layer to block the leaching of arsenic-containing substances in the waste residue inner core layer through a physical barrier. At the same time, the hybrid gel network makes the barrier coating layer formulation system have the acid and alkali resistance of sodium aluminosilicate gel, endowing the barrier coating layer with high acid and alkali resistance, so that even in acidic and alkaline environments, AsO4 3- in the arsenic-containing waste residue is not easily dissolved and released, which is also beneficial to reducing the leaching toxicity of arsenic. In addition, the hybrid gel network can not only make the barrier coating layer formulation system have the cementation strength of calcium aluminosilicate gel, but also endow the barrier coating layer with high density, which is also beneficial to improving the strength of the barrier coating layer, thereby being beneficial to improving the strength of the barrier coating layer.

[0053] Again, the raw materials for the paving stones in this technical solution include carbide slag, desulfurized gypsum, mineral powder, core-shell waste residue particles, fine aggregate, and water. Carbide slag is a by-product formed when calcium carbide reacts with water to produce acetylene. Ca(OH)2 in carbide slag can form an alkaline environment. SiO2 in the mineral powder exists in the form of a silicon-oxygen network structure, and Al2O3 in the mineral powder exists in the form of an aluminum-oxygen network structure. In an alkaline environment, the silicon-oxygen chains in the silicon-oxygen network structure and the aluminum-oxygen chains in the aluminum-oxygen network structure both depolymerize, generating silicate ions and aluminate ions respectively. The silicate ions can react with Ca(OH)2, the product after the activation of the activity of CaO in the mineral powder in the system, to form calcium silicate gel mainly in a layered structure. And in this system, aluminate ions replace silicate ions and enter the interior of the calcium silicate gel to form calcium aluminosilicate gel. The calcium aluminosilicate gel can adhere to the surfaces of the core-shell waste residue particles (acting as coarse aggregate) and the fine aggregate and wrap and bond the core-shell waste residue particles and the fine aggregate, enabling the paving stones to bond into a whole and ensuring the strength of the paving stones.

[0054] Meanwhile, the calcium aluminosilicate gel formed in this application has a nano-particle stacking structure, and its structure is denser than the gel formed by cement, which is beneficial to improving the strength of the paving stones. Further, the denser calcium aluminosilicate gel is beneficial to improving the tensile strength of the paving stones, and the stress generated during the crystallization process of ettringite is smaller than that of arsenical ettringite. This makes it so that even if ettringite is formed in the paving stone formulation system, the relatively low stress generated during the crystallization process of ettringite is not easily exceeded the tensile strength to form through cracks, thus being beneficial to ensuring the strength of the paving stones.

[0055] In addition, desulfurized gypsum is a by-product of industrial flue gas desulfurization in coal-fired power plants, steel plants, etc. (mainly using the limestone-gypsum wet desulfurization process). In an alkaline environment, calcium sulfate dihydrate in desulfurized gypsum dissolves and gradually releases sulfate ions and Ca 2+ , in addition, carbide slag can also provide Ca 2+ . In an aqueous and alkaline environment, sulfate ions, aluminate ions, and Ca 2+ react to form ettringite, and the ettringite can fill the pores of the paving stones, enhancing the compactness, thereby improving the strength of the paving stones.

[0056] In addition, the core-shell waste residue particles with relatively high strength are mutually interlocked to form the framework of the paving stones, providing the function of supporting the paving stones, which is beneficial to endowing the paving stones with mechanical properties such as high flexural strength and compressive strength; meanwhile, the fine aggregate can fill the voids in the paving stones, improve the compactness of the paving stones, reduce the risk of shrinkage and cracking, and thus enhance the mechanical properties such as compressive strength and flexural strength of the paving stones.

[0057] In summary, the above-mentioned various effects in this application are beneficial to ensuring the mechanical properties such as compressive strength and flexural strength of the paving stones.

[0058] Furthermore, in this technical solution, the waste residue core layer itself can fix arsenic by forming insoluble precipitates of AsO4 3- and adsorbing and fixing AsO4 3- ; while the barrier coating layer can block the leaching of AsO4 3- in the waste residue core layer through physical and chemical actions, further realizing the immobilization of AsO4 3- . The combined action of the above two aspects results in extremely low leaching of AsO4 3- in the core-shell waste residue particles. Therefore, the situation where AsO4 3- replaces the sulfate radical in ettringite in this technical solution can be ignored, and the ettringite formed in this technical solution is basically ordinary ettringite. Compared with arsenic-type ettringite, the volume expansion of ordinary ettringite is relatively low, which can stably fill the pores, avoiding the significant volume expansion during the crystallization growth of arsenic-type ettringite, which may lead to the formation of local stress concentration inside the material and easily cause the generation of through cracks, thereby preventing water and harmful substances from invading the interior of the paving stone, which is beneficial to improving the durability of the paving stone.

[0059] Meanwhile, due to the strong bonding effect between sulfate ions and Ca 2+ and Al 3+ in ordinary ettringite, ordinary ettringite is not easily decomposed in an acidic environment, which is also beneficial to avoiding the extremely rapid decomposition of arsenic-type ettringite in an acidic environment and preventing the problem of the decline in the durability of the paving stone.

[0060] In addition, as described above, since the calcium aluminosilicate gel formed in this technical solution has a nano-particle accumulation structure and its structure is relatively dense, the paving stone of this technical solution is not easily formed with through cracks, which is also beneficial to ensuring the durability of the paving stone. In addition, the filling effect of the fine aggregate and the skeleton effect of the core-shell waste residue particles in this technical solution are also beneficial to ensuring the durability of the paving stone.

[0061] In summary, the present application is beneficial to ensuring the durability of the paving stone through the above-mentioned multiple aspects.

[0062] Therefore, by treating the arsenic-containing waste residue, this technical solution not only turns waste into treasure and makes full use of the arsenic-containing waste residue, but also fixes AsO4 3- in the arsenic-containing waste residue, so that the paving stone has excellent and persistent extremely low arsenic leaching toxicity. At the same time, the core-shell waste residue particles prepared by this technical solution have extremely high strength. Adding them to the paving stone formula is not only beneficial to reducing costs, but also enables the paving stone to have mechanical properties such as higher flexural strength and compressive strength. In addition, by optimizing the paving stone formula and basically no arsenic-type ettringite is generated in the paving stone formula, it is beneficial to improve the durability of the paving stone to meet the use requirements.

[0063] It should be noted that the raw material phosphate in the waste residue core layer of this solution can be potassium phosphate, sodium phosphate, ammonium phosphate, etc., and the specific types are not limited here.

[0064] Preferably, calculated by mass percentage, the mineral components of the arsenic-containing waste residue include 5-30% arsenopyrite, 10-50% pyrite, 20-60% quartz, and 1-15% secondary arsenate.

[0065] Preferably, the particle size of the waste residue core layer is 5-10 mm, and the thickness of the barrier coating layer is 2-3 mm.

[0066] This technical solution limits the particle size of the waste residue core layer and the thickness of the coating layer, which is not only beneficial to ensuring the strength of the core-shell waste residue particles and the fixing effect on AsO4 3- but also beneficial to ensuring its strength, thus being beneficial to ensuring the performance of the paving stone.

[0067] Preferably, the fine aggregate is any one of granite, limestone, and feldspar, and the particle size of the fine aggregate is 0.075-0.3 mm.

[0068] Granite, limestone, and feldspar are all hard rocks, and their fine aggregates can significantly improve the mechanical properties such as the compressive strength and flexural strength of the paving stone. In addition, the fine aggregate with a particle size of 0.075-0.3 mm can effectively fill the voids between the coarse aggregates, reduce the porosity inside the paving stone, improve the density, thereby reducing the accumulation of damage during freeze-thaw cycles and improving the durability.

[0069] Preferably, the magnesium oxide is light-burned magnesium oxide.

[0070] Compared with ordinary magnesium oxide, light-burned magnesium oxide has higher reaction activity and is more conducive to reacting with raw materials such as mineral powder and slag powder. Therefore, this technical solution preferably uses light-burned magnesium oxide as the magnesium oxide.

[0071] Furthermore, calculated by mass parts, the paving stone includes the following raw materials: 4.5-6 parts of carbide slag, 2.5-3.5 parts of desulfurized gypsum, 20-23 parts of mineral powder, 31-34 parts of core-shell waste residue particles, 26-30 parts of fine aggregate, and 7-8 parts of water;

[0072] Calculated by mass parts, the waste residue core layer includes the following raw materials: 8-10 parts of magnesium oxide, 15-20 parts of mineral powder, 15-20 parts of slag powder, 5-8 parts of red mud, 40-60 parts of arsenic-containing waste residue, 0.1-0.5 parts of phosphate, and 7-10 parts of water.

[0073] This technical solution limits the raw material ratio of the paving stone and the raw material ratio of the waste residue core layer, which is beneficial to ensuring the performance of the paving stone.

[0074] Further explanation: the particle size of the arsenic-containing waste residue is < 75 μm, and the specific surface area is > 350 m 2 / g.

[0075] The smaller the particle size of the arsenic-containing waste residue and the larger the specific surface area, the more beneficial it is to increase the exposure of AsO4 in the arsenic-containing waste residue and be stabilized, thus facilitating the reduction of the arsenic leaching concentration. However, when the particle size is continuously reduced and the specific surface area is increased, the improvement effect is limited, and the production cost is easily increased. Therefore, in this technical solution, the particle size of the arsenic-containing waste residue is limited to < 75 μm, and the specific surface area is limited to > 350 m 3- / g, which is beneficial to reducing the arsenic leaching concentration at a lower cost and making the obtained paving stones meet the usage requirements. 2 Further explanation: calculated by mass percentage, the chemical components of the slag powder in the waste residue inner core layer and the barrier coating layer both include 40 - 55% of SiO2, 24 - 28% of Al2O3, 5 - 7% of Fe2O3, and 5 - 8% of CaO, and the rest is the loss on ignition.

[0076] This technical solution preferably adds slag powder with a SiO2 content of 45 - 60% and an Al2O3 content of 25 - 30% calculated by mass percentage to the waste residue inner core layer and the barrier coating layer formulations, which is beneficial to increasing the amount of gel formed in these two formulation systems of the waste residue inner core layer and the barrier coating layer, thereby facilitating the improvement of the strength of the paving stones and the reduction of the arsenic leaching content.

[0077] Preferably, calculated by mass percentage, the chemical components of the slag powder in the waste residue inner core layer and the barrier coating layer both include 54% of SiO2, 26.3% of Al2O3, 6.5% of Fe2O3, 7.2% of CaO, and 0.9% of MgO, and the rest is the loss on ignition.

[0078] Further explanation: calculated by mass percentage, the chemical components of the red mud include 15 - 20% of Al2O3, 5 - 15% of SiO2, 30 - 40% of Fe2O3, 5 - 10% of CaO, and 5 - 10% of Na2O, and the rest is the loss on ignition.

[0079] This technical solution preferably adds red mud with a CaO content of 5 - 10% calculated by mass percentage to the waste residue inner core layer formulation system, which is beneficial to improving the alkaline environment in the waste residue inner core layer system and promoting the depolymerization of Al2O3 and SiO2 in the mineral powder and slag powder. The depolymerized products form hydrated magnesium silicate with a layered structure, aluminum magnesium hydrotalcite, and a hybrid gel network structure under alkaline conditions. Hydrated magnesium silicate, aluminum magnesium hydrotalcite, and the hybrid gel network structure can all react with AsO4

[0080] 3- ​Fixation reduces the arsenic leaching concentration of the paving stones. In addition, the formation of the mixed gel network structure is also beneficial to improving the strength of the paving stones.

[0081] Further illustration, the modulus of the sodium silicate is 1.2 - 1.4.

[0082] The modulus of sodium silicate refers to the molar ratio of SiO2 to Na2O in its molecule. When the modulus of sodium silicate is 1.2 - 1.4, the free OH - produced by the hydrolysis of sodium silicate is relatively large, promoting the full depolymerization of Al2O3 and SiO2 in the mineral powder and slag powder, thus promoting the formation of calcium aluminosilicate gel and sodium aluminosilicate gel in the barrier coating, which is beneficial to ensuring the performance of the barrier coating.

[0083] Further illustration, calculated by mass percentage, the chemical composition of the carbide slag includes 85 - 90% Ca(OH)2, 3 - 3.5% SiO2, 0.8 - 1% Fe2O3, 2 - 2.5% Al2O3, and 0.8 - 1% MgO, and the rest is the loss on ignition.

[0084] This technical solution preferably adds carbide slag with a Ca(OH)2 content of 85 - 90% calculated by mass percentage to the paving stone formula, so that the OH - generated in the paving stone formula system is sufficient, thus fully activating the activity of the mineral powder and generating calcium aluminosilicate gel to ensure the performance of the product.

[0085] Further illustration, the flexural strength of the paving stone ≥ 5 MPa, the compressive strength ≥ 48 MPa, the arsenic leaching concentration before soaking in acetic acid buffer solution with pH 2.88 ≤ 0.2 mg / L, and the arsenic leaching concentration after soaking in acetic acid buffer solution with pH 2.88 for 30 days ≤ 0.3 mg / L.

[0086] Both the frost resistance test and the water erosion resistance test are important means to evaluate the durability of the paving stones. The paving stones of this technical solution have reached the qualified standard in both the frost resistance test and the water erosion resistance test, fully proving that the paving stones of this technical solution have good durability. At the same time, the arsenic leaching concentration of the paving stones of this technical solution before soaking in acetic acid buffer solution with pH 2.88 ≤ 0.2 mg / L, and the arsenic leaching concentration after soaking in acetic acid buffer solution with pH 2.88 for 30 days ≤ 0.3 mg / L. The paving stones of this technical solution have excellent and persistent extremely low arsenic leaching toxicity. In addition, the flexural strength of this technical solution ≥ 5 MPa, the compressive strength ≥ 48 MPa, with high mechanical properties. Therefore, the paving stones prepared by this technical solution, while applying arsenic-containing waste residue to the paving stones and reducing production costs, not only have excellent and persistent extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of the paving stones.

[0087] A preparation method of paving stones added with arsenic-containing waste residue, which is used to prepare the paving stones added with arsenic-containing waste residue as described above, comprises the following steps:

[0088] A. Prepare core-shell waste residue particles;

[0089] Mix the formulated amounts of magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizing machine, and obtain a waste residue inner core layer after drying;

[0090] Mix the formulated amounts of slag powder, mineral powder, sodium silicate and water evenly to obtain a barrier coating slurry;

[0091] Immerse the waste residue inner core layer in the barrier coating slurry, take it out, and after steam curing and room temperature curing, form a barrier coating layer on the surface of the waste residue inner core layer to obtain core-shell waste residue particles;

[0092] B. Prepare paving stones:

[0093] Mix the formulated amounts of carbide slag, desulfurized gypsum, mineral powder and water evenly to obtain a gel material;

[0094] Mix the core-shell waste residue particles, fine aggregate and the gel material evenly to obtain a paving stone slurry; pour the paving stone slurry into a mold, and obtain a plate after vibration compaction; after sealing the plate and performing steam curing and room temperature curing, obtain paving stones.

[0095] This technical solution also proposes a preparation method of paving stones added with arsenic-containing waste residue, the steps of which are simple, highly operable, and are beneficial to avoiding the relevant properties of paving stones during the preparation process.

[0096] Specifically, in this technical solution, when preparing the paving stone slurry, part of the water is used to wet the core-shell waste residue particles and the fine aggregate first, so that the core-shell waste residue particles and the fine aggregate are more easily wrapped and adhered by the cementitious material, thereby ensuring the strength of the paving stones.

[0097] Further explanation, in steps A and B, the curing temperature of the steam curing is 60-70°C, and the curing time is 48-74h; the curing time of the room temperature curing is 168-240h.

[0098] This technical solution limits the temperature and time of steam curing and the time of room temperature curing, improves the density of the product, reduces fine pores, and improves the mechanical properties and durability of the product.

[0099] The technical solution of the present invention will be further described below through specific embodiments.

[0100] Test method:

[0101] Flexural strength: The flexural performance was tested according to the test method of "GB / T 28635-2012 Concrete Pavement Bricks".

[0102] Compressive strength: The compressive strength was tested according to the test method of "GB / T 28635-2012 Concrete Pavement Bricks".

[0103] Freeze-thaw test: The freeze-thaw resistance test was carried out according to the test method in Appendix E of "GB / T 28635-2012 Concrete Pavement Bricks". If there are basically no cracks on the surface of the paving stone after 50 freeze-thaw cycles, the mass loss rate < 5%, and the compressive strength loss < 25%, it is qualified.

[0104] ‌Water erosion resistance: The paving stone was soaked in water at 20±2°C for 48h, taken out and dried in an oven at 60±5°C for 48h. The above soaking and drying steps were repeated 50 times. Then, visually check the cracks on the surface of the paving stone, and measure the mass, compressive strength and flexural strength of the paving stone. If there are basically no cracks on the surface of the paving stone, the mass loss rate < 5%, and the loss rates of compressive strength and flexural strength are both < 25%, it is qualified.

[0105] Arsenic leaching concentration before soaking: The arsenic leaching concentration of the paving stone without being soaked in acetic acid buffer solution with pH 2.88 was tested according to the test method of "GB18598-2019 Hazardous Waste Identification Standard - Identification of Leaching Toxicity". If the arsenic leaching concentration ≤ 0.2mg / L, it is qualified. Among them, the preparation method of acetic acid buffer solution with pH 2.88 is: add 5.7mL glacial acetic acid to 500mL deionized water. Add 64.3mL 1mol / L NaOH solution, and make up the volume to 1L with deionized water. Finally, adjust the pH to 2.88 (fine-tune with acetic acid or NaOH).

[0106] Arsenic leaching concentration after soaking: The arsenic leaching concentration of the paving stone soaked in acetic acid buffer solution with pH 2.88 for 30 days was tested according to the test method of "GB18598-2019 Hazardous Waste Identification Standard - Identification of Leaching Toxicity". If the arsenic leaching concentration ≤ 0.3mg / L, it is qualified.

[0107] In the examples and comparative examples of the present invention, calculated by mass percentage, the mineral components of the arsenic-containing waste residue include 25% arsenopyrite, 30% pyrite, 40% quartz and 5% secondary arsenate.

[0108] Calculated by mass percentage, the chemical components of the slag powder in the inner core layer and the barrier coating layer of the waste residue both include 54% SiO2, 26.3% Al2O3, 6.5% Fe2O3, 7.2% CaO and 0.9% MgO, and the rest is the loss on ignition.

[0109] The mineral composition of red mud includes goethite. Calculated by mass percentage, the chemical composition of red mud includes 18% Al2O3, 13% SiO2, 35% Fe2O3, 8% CaO, and 8% Na2O, and the rest is loss on ignition.

[0110] Calculated by mass percentage, the chemical composition of the carbide slag includes 87% Ca(OH)2, 3% SiO2, 0.9% Fe2O3, 2% Al2O3, and 0.9% MgO, and the rest is loss on ignition.

[0111] Example 1

[0112] In this example, calculated by mass parts, it includes the following raw materials: 5 parts of carbide slag, 3 parts of desulfurized gypsum, 20 parts of ore powder, 31 parts of core-shell waste residue particles, 26 parts of granite with a particle size of 0.075 mm, and 7 parts of water;

[0113] The core-shell waste residue particles sequentially include a waste residue inner core layer and a barrier coating layer from the inside to the outside;

[0114] Calculated by mass parts, the waste residue inner core layer includes the following raw materials: 8 parts of light-burned magnesium oxide, 15 parts of ore powder, 15 parts of slag powder, 6 parts of red mud, 50 parts of arsenic-containing waste residue, 0.3 part of potassium phosphate, and 7 parts of water; the particle size of the arsenic-containing waste residue is 35 μm, and the specific surface area is 380 m 2 / g;

[0115] Calculated by mass parts, the barrier coating layer includes the following raw materials: 45 parts of slag powder, 38 parts of ore powder, 7 parts of sodium silicate with a modulus of 1.2, and 5 parts of water.

[0116] The preparation method of the paving stone adding arsenic-containing waste residue in this example includes the following steps:

[0117] A. Prepare core-shell waste residue particles;

[0118] Mix the formulated amount of light-burned magnesium oxide, ore powder, slag powder, red mud, arsenic-containing waste residue, phosphate, and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizing machine, and after drying, obtain a waste residue inner core layer with a particle size of 5 mm;

[0119] Mix the formulated amount of slag powder, ore powder, sodium silicate, and water evenly to obtain a barrier coating slurry;

[0120] Immerse the waste residue inner core layer in the barrier coating slurry, take it out, cure it in 60 °C steam for 50 h and cure it at room temperature for 168 h, and then form a barrier coating layer with a thickness of 2 mm on the surface of the waste residue inner core layer to obtain core-shell waste residue particles with a particle size of 7 mm;

[0121] B. Prepare paving stones:

[0122] Mix the formula amount of carbide slag, desulfurized gypsum, mineral powder and water evenly to obtain a gel material;

[0123] Mix the core-shell waste residue particles, fine aggregate and gel material evenly to obtain paving stone slurry; pour the paving stone slurry into a mold, and obtain a plate after vibrating and pressing for 0.5 min; seal the plate and cure it in steam at 60 °C for 50 h and cure it at room temperature for 168 h to obtain paving stones.

[0124] Example 2

[0125] In this example, calculated by mass fraction, it includes the following raw materials: 5 parts of carbide slag, 3.5 parts of desulfurized gypsum, 22 parts of mineral powder, 34 parts of core-shell waste residue particles, 28 parts of limestone with a particle size of 0.1 mm and 7 parts of water;

[0126] The core-shell waste residue particles include a waste residue inner core layer and a barrier coating layer from the inside to the outside in sequence;

[0127] Calculated by mass fraction, the waste residue inner core layer includes the following raw materials: 10 parts of light-burned magnesia, 20 parts of mineral powder, 18 parts of slag powder, 6 parts of red mud, 50 parts of arsenic-containing waste residue, 0.2 part of sodium phosphate and 8 parts of water; the particle size of the arsenic-containing waste residue is 25 μm, and the specific surface area is 400 m 2 / g;

[0128] Calculated by mass fraction, the barrier coating layer includes the following raw materials: 50 parts of slag powder, 38 parts of mineral powder, 8 parts of sodium silicate with a modulus of 1.3 and 5 parts of water.

[0129] The preparation method of the paving stone added with arsenic-containing waste residue in this example includes the following steps:

[0130] A. Prepare core-shell waste residue particles;

[0131] Mix the formula amount of light-burned magnesia, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water evenly to obtain a waste residue modified mixture; send the waste residue modified mixture into a pelletizer, and obtain a waste residue inner core layer with a particle size of 8 mm after drying;

[0132] Mix the formula amount of slag powder, mineral powder, sodium silicate and water evenly to obtain a barrier coating slurry;

[0133] Soak the waste residue inner core layer in the barrier coating slurry, take it out and cure it in steam at 65 °C for 48 h and cure it at room temperature for 240 h, and a barrier coating layer with a thickness of 3 mm is formed on the surface of the waste residue inner core layer to obtain core-shell waste residue particles with a particle size of 11 mm;

[0134] B. Prepare paving stones:

[0135] Mix the formula amount of carbide slag, desulfurized gypsum, mineral powder and water evenly to obtain a gel material;

[0136] Mix the core-shell waste residue particles, fine aggregate and gel material evenly to obtain the paving stone slurry; pour the paving stone slurry into a mold, and obtain the plate after vibrating and pressing for 0.6 min; seal the plate and cure it in steam at 65 °C for 48 h and cure it at room temperature for 240 h to obtain the paving stone.

[0137] Example 3

[0138] In this example, calculated by mass fraction, it includes the following raw materials: 6 parts of carbide slag, 2.5 parts of desulfurized gypsum, 20 parts of mineral powder, 32 parts of core-shell waste residue particles, 30 parts of feldspar with a particle size of 0.3 mm, and 7.5 parts of water;

[0139] The core-shell waste residue particles successively include a waste residue inner core layer and a barrier coating layer from the inside to the outside;

[0140] Calculated by mass fraction, the waste residue inner core layer includes the following raw materials: 10 parts of light-burned magnesia, 17 parts of mineral powder, 15 parts of slag powder, 6 parts of red mud, 45 parts of arsenic-containing waste residue, 0.1 part of ammonium phosphate, and 7 parts of water; the particle size of the arsenic-containing waste residue is 40 μm, and the specific surface area is 370 m 2 / g;

[0141] Calculated by mass fraction, the barrier coating layer includes the following raw materials: 45 parts of slag powder, 37 parts of mineral powder, 7 parts of sodium silicate with a modulus of 1.2, and 6 parts of water.

[0142] The preparation method of the paving stone adding arsenic-containing waste residue in this example includes the following steps:

[0143] A. Prepare the core-shell waste residue particles;

[0144] Mix the formula amount of light-burned magnesia, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water evenly to obtain the waste residue modified mixture; send the waste residue modified mixture into a pelletizer, and obtain the waste residue inner core layer with a particle size of 10 mm after drying;

[0145] Mix the formula amount of slag powder, mineral powder, sodium silicate and water evenly to obtain the barrier coating slurry;

[0146] Immerse the waste residue inner core layer in the barrier coating slurry, take it out and cure it in steam at 70 °C for 48 h and cure it at room temperature for 200 h, and a barrier coating layer with a thickness of 2 mm is formed on the surface of the waste residue inner core layer to obtain core-shell waste residue particles with a particle size of 12 mm;

[0147] B. Prepare the paving stone:

[0148] Mix the formula amount of carbide slag, desulfurized gypsum, mineral powder and water evenly to obtain the gel material;

[0149] Mix the core-shell waste residue particles, fine aggregate and gel material evenly to obtain the paving stone slurry; pour the paving stone slurry into a mold and vibrate and press for 0.8 min to obtain a plate; seal the plate and cure it in steam at 70 °C for 48 h and at room temperature for 200 h to obtain the paving stone.

[0150] Comparative Example 1

[0151] Prepare the paving stone by using the existing preparation method, that is, mix 10 parts of lime, 20 parts of polymeric ferric sulfate, 15 parts of dolomite sand, 15 parts of cement and 30 parts of water evenly to obtain a composite curing agent, and mix 30 parts of the composite curing agent with 40 parts of arsenic-containing waste residue evenly to obtain the paving stone slurry. Pour the paving stone slurry into a mold and vibrate and press for 0.5 min to obtain a plate; seal the plate and cure it in steam at 60 °C for 48 h and at room temperature for 168 h to obtain the paving stone.

[0152] Comparative Example 2

[0153] The preparation method and raw materials of Comparative Example 2 are the same as those of Example 2, except that in Comparative Example 2, light-burned magnesium oxide is not added to the formula of the inner core layer of the waste residue.

[0154] Comparative Example 3

[0155] The preparation method and raw materials of Comparative Example 3 are the same as those of Example 2, except that in Comparative Example 3, a barrier coating layer is not formed on the surface of the inner core layer of the waste residue, that is, the core-shell waste residue particles in Comparative Example 3 only include the inner core layer of the waste residue.

[0156] Comparative Example 4

[0157] The preparation method and raw materials of Comparative Example 4 are the same as those of Example 2, except that in Comparative Example 4, sodium silicate is not added to the formula of the barrier coating layer.

[0158] Comparative Example 5

[0159] The preparation method and raw materials of Comparative Example 5 are the same as those of Example 2, except that in Comparative Example 5, core-shell waste residue particles are not added to the paving stone formula.

[0160] Conduct performance tests on the paving stones prepared in the above examples and comparative examples, and the specific test results are shown in Table 1.

[0161] Table 1 Related performance test results of paving stones

[0162]

[0163] Both the frost resistance test and the water erosion resistance test are important means to evaluate the durability of paving stones. It can be seen from the test data in Table 1 that the paving stones prepared by this technical solution meet the qualified standards in both the frost resistance test and the water erosion resistance test, fully demonstrating that the paving stones of this technical solution have good durability. At the same time, the arsenic leaching concentration of the paving stones of this technical solution before being soaked in the acetic acid buffer solution with a pH of 2.88 is ≤0.2 mg / L, and the arsenic leaching concentration after being soaked in the acetic acid buffer solution with a pH of 2.88 for 30 days is ≤0.3 mg / L. The paving stones of this technical solution have excellent and persistent extremely low arsenic leaching toxicity. In addition, the flexural strength of this technical solution is ≥5 MPa, and the compressive strength is ≥48 MPa, with relatively high mechanical properties. Furthermore, through comparative experiments, it is found that the paving stones obtained by using this technical solution (i.e., a preparation method of paving stones adding arsenic-containing waste residue) are superior to the paving stones in Comparative Example 1 (i.e., the prior art) in terms of various performance test indicators. Therefore, the paving stones obtained by the preparation method of paving stones adding arsenic-containing waste residue of this technical solution not only have excellent and persistent extremely low arsenic leaching toxicity, but also can improve the mechanical properties and durability of paving stones on the premise of applying arsenic-containing waste residue to paving stones and reducing production costs.

[0164] In Comparative Example 2, since light-burned magnesium oxide was not added to the waste residue inner core layer formula, magnesium oxide could not hydrolyze to generate magnesium ions that could individually fix arsenate. In addition, due to the lack of magnesium ions in the waste residue inner core layer formula system, it also led to the inability to generate magnesium silicate hydrate and arsenic acid intercalated aluminum magnesium hydrotalcite that could fix arsenate in the waste residue inner core layer formula, resulting in a worse fixing effect on arsenate and thus an increase in arsenic leaching concentration.

[0165] In Comparative Example 3, due to the absence of a barrier coating layer, the following defects occurred in many aspects: (1) The barrier coating layer could have enhanced the core-shell waste residue particles and improved the mechanical properties such as flexural and compressive strength of the paving stones. However, due to the absence of this structure, the mechanical properties of the paving stones decreased. (2) The barrier coating layer had the ability to fix arsenate. Without this barrier coating layer, the arsenate in the waste residue inner core layer was likely to undergo a substitution reaction with the sulfate ions in ettringite, generating arsenic-type ettringite, which not only further decreased the mechanical properties of the paving stones but also led to a decrease in its durability. (3) The absence of the fixing effect of the barrier coating layer on arsenate reduced the stability of arsenate in the paving stones and increased the arsenic leaching concentration. In addition, the barrier coating layer had acid and alkali resistance characteristics and could inhibit the leaching of arsenate in acidic or alkaline environments. Without setting this coating layer, the arsenic leaching concentration of the paving stones in acidic or alkaline environments increased significantly.

[0166] In Comparative Example 4, since sodium silicate is not added to the barrier coating formula, it is impossible to alkaline-excite the mineral powder and slag powder in the barrier coating to form a mixed gel network composed of calcium aluminum silicate gel and sodium aluminum silicate gel, which results in the barrier coating failing to achieve the barrier coating's reinforcing effect on the core-shell waste slag particles, causing the mechanical properties of the paving stones, such as flexural strength and compressive strength, to deteriorate. At the same time, the barrier coating's fixation of arsenate also depends on its internal gel network structure. Since the gel network cannot be formed, the barrier coating cannot effectively fix the arsenate, making it easy for the arsenate in the inner core layer of the waste slag to undergo a substitution reaction with the sulfate ions in the calcium sulfonate to form arsenic-type calcium sulfonate, which not only further weakens the mechanical properties of the paving stones, but also affects their durability. In addition, since the barrier coating cannot effectively fix the arsenate, the arsenic element in the paving stones is more easily leached, resulting in an increase in the arsenic leaching concentration. At the same time, the barrier coating layer that has not formed an effective gel network has also lost its original acid and alkali resistance, causing the arsenic leaching concentration of the paving stones in an acidic or alkaline environment to increase significantly.

[0167] In Comparative Example 5, since the core-shell waste particles were not added to the paving stone formula, the strength and durability of the paving stones deteriorated.

[0168] The technical principle of the present invention is described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the scope of protection of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without paying creative labor, and these methods will fall within the scope of protection of the present invention.

Claims

1. A paving stone with arsenic-containing waste residue added, characterized in that: Calculated by weight, the raw materials include: 4.5-6 parts of carbide slag, 2.5-3.5 parts of desulfurized gypsum, 20-23 parts of mineral powder, 31-34 parts of core-shell waste slag particles, 26-30 parts of fine aggregate and 7-8 parts of water; wherein the particle size of the core-shell waste slag particles is 7-13 mm; calculated by weight percentage, the content of calcium hydroxide in the carbide slag is ≥8%; The core-shell waste slag particles include a waste slag core layer and a barrier wrapping layer from the inside to the outside; Calculated by weight, the inner core layer of the waste slag includes the following raw materials: 8-10 parts of magnesium oxide, 15-20 parts of mineral powder, 15-20 parts of slag powder, 5-8 parts of red mud, 40-60 parts of arsenic-containing waste slag, 0.1-0.5 parts of phosphate and 7-10 parts of water; wherein the mineral components of the arsenic-containing waste slag include arsenopyrite; the mineral components of the red mud include goethite, and the chemical components of the red mud include CaO; Calculated by weight, the barrier wrapping layer includes the following raw materials: 45-50 parts of slag powder, 35-42 parts of mineral powder, 7-8 parts of sodium silicate and 5-6 parts of water; The chemical compositions of the slag powder in the waste slag inner core layer and the barrier wrap layer include SiO2, Al2O3 and CaO.

2. The paving stone with arsenic-containing waste residue added according to claim 1, characterized in that: The particle size of the arsenic-containing waste residue is less than 75 μm, and the specific surface area is greater than 350 m 2 / g.

3. The paving stone added with arsenic-containing waste slag according to claim 1, characterized in that: Calculated by mass percentage, the chemical composition of the slag powder in the waste slag inner core layer and the barrier wrap layer includes SiO2 40-55%, Al2O3 24-28%, Fe2O3 5-7% and CaO 5-8%, and the rest is ignition loss.

4. The paving stone with arsenic-containing waste residue added according to claim 1, characterized in that: Calculated by mass percentage, the chemical composition of the red mud includes Al2O3 15-20%, SiO2 5-15%, Fe2O3 30-40%, CaO 5-10% and Na2O 5-10%, and the rest is ignition loss.

5. The paving stone added with arsenic-containing waste residue according to claim 1, characterized in that: The modulus of the sodium silicate is 1.2 to 1.

4.

6. The paving stone added with arsenic-containing waste slag according to claim 1, characterized in that: Calculated by mass percentage, the chemical composition of the carbide slag includes Ca(OH)2 85-90%, SiO2 3-3.5%, Fe2O3 0.8-1%, Al2O3 2-2.5% and MgO 0.8-1%, and the rest is loss on ignition.

7. The paving stone added with arsenic-containing waste residue according to claim 1, characterized in that: The flexural strength of the paving stone is ≥5MPa, the compressive strength is ≥48MPa, the arsenic leaching concentration before being soaked in an acetic acid buffer solution with a pH of 2.88 is ≤0.2mg / L, and the arsenic leaching concentration after being soaked in an acetic acid buffer solution with a pH of 2.88 for 30 days is ≤0.3mg / L.

8. A method for preparing paving stones with arsenic-containing waste residue, characterized in that: The method for preparing the paving stone added with arsenic-containing waste residue as claimed in any one of claims 1 to 7 comprises the following steps: A. Preparation of core-shell waste particles: The magnesium oxide, mineral powder, slag powder, red mud, arsenic-containing waste residue, phosphate and water are mixed evenly to obtain a waste residue modified mixture; the waste residue modified mixture is fed into a pelletizing machine, and after drying, a waste residue inner core layer is obtained; The slag powder, mineral powder, sodium silicate and water in the formula are evenly mixed to obtain a barrier coating slurry; The waste slag inner core layer is immersed in a barrier coating slurry, taken out and subjected to steam curing and room temperature curing, so that a barrier coating layer is formed on the surface of the waste slag inner core layer to obtain core-shell waste slag particles; B. Preparation of floor paving stones: Evenly mixing the formulated amounts of carbide slag, desulfurized gypsum, mineral powder and water to obtain a gel material; The core-shell waste particles, fine aggregates and gel materials are uniformly mixed to obtain floor paving stone slurry; the floor paving stone slurry is poured into a mold and vibrated to obtain a board; the board is sealed and subjected to steam curing and room temperature curing to obtain the floor paving stone.

9. The method for preparing paving stones with arsenic-containing waste residue added according to claim 8, characterized in that: In step A and step B, the curing temperature of the steam curing is 60-70° C., and the curing time is 48-74 hours; the curing time of the room temperature curing is 168-240 hours.

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