Lithium slag powder-based multi-element solid waste low-carbon concrete and preparation method thereof

Abstract

This invention discloses a lithium slag powder-based multi-component solid waste low-carbon concrete and its preparation method, belonging to the field of low-carbon concrete manufacturing technology. The raw materials for the concrete include: cement, fly ash, lithium slag powder, iron tailings sand, recycled aggregate, limestone crushed stone, water-reducing agent, water, humic acid, and hydroxypropyl guar gum. The lithium slag powder forms a core-shell structure with acid-process lithium slag as the core and an alkali-process lithium slag slurry coated on the core surface. Through the acid-alkali lithium slag gradient mineralization core-shell structure design and the synergistic effect of multiple concrete components, utilizing lithium slag powder modification and concrete rheological property optimization, and cement-based microstructure control, the working and mechanical properties and environmental safety of the lithium slag powder-based multi-component solid waste concrete are improved, achieving efficient and high-value utilization of bulk solid waste.

Description

Technical Field

[0001] This invention relates to the field of low-carbon concrete manufacturing technology, and in particular to a method for preparing lithium slag powder-based multi-element solid waste low-carbon concrete. Background Technology

[0002] In recent years, the utilization of industrial solid waste in building materials has become an important path to promote green and low-carbon development. At the same time, the rapid development of new energy vehicles and energy storage industries has also brought new challenges to solid waste management. Taking lithium carbonate production as an example, the current annual output in China is close to one million tons, while producing one ton of lithium salt generates approximately 8-10 tons of lithium slag. Therefore, it is urgent to explore ways to utilize lithium slag on a large scale and at high value.

[0003] Utilizing lithium slag as a concrete admixture for resource recovery is technically feasible. Lithium slag is milky white in appearance and its chemical composition is highly similar to clay, mainly containing amorphous SiO2 and Al2O3. Lithium slag particles have a porous structure, a large specific surface area, and good pozzolanic activity, micro-expansion, and grindability. When used as a cementitious admixture or mineral admixture in concrete preparation, it can effectively improve the compressive strength of concrete, enhance shrinkage crack resistance, and improve the microstructure of hydration products. From an environmental perspective, replacing part of the cement with lithium slag can significantly reduce carbon emissions during concrete production, making it an effective way to promote green and low-carbon construction.

[0004] Lithium slag is mainly divided into two sources: spodumene acid process lithium slag (i.e., "acid process lithium slag") and lepidolite alkaline process lithium slag (i.e., "alkaline process lithium slag"). While their main components are the same, the types, structures, and reaction characteristics of their minor components differ. Acid process lithium slag undergoes more thorough lattice destruction during acid leaching, resulting in a higher proportion of amorphous SiO2 / Al2O3, a more pronounced porous and layered structure, and residual SO3 / SO4. 2- Higher concentrations of alkali-process lithium slag result in more complex mineral phases, higher content of some alkali metals, superior early pozzolanic activity, and relatively higher levels of CaO or free Ca(OH)2. However, the following significant drawbacks still exist when using acid-process and alkali-process lithium slag directly as concrete raw materials.

[0005] (1) Workability and limitations of high dosage. Lithium slag has not undergone any treatment, and its porous structure, high water absorption and large water demand have not been effectively improved. When the dosage is ≥30%, the fluidity and slump loss of concrete will be significantly deteriorated, which will easily affect the pumping performance during construction. Existing technologies rarely optimize the workability of lithium slag concrete, thus limiting its high dosage utilization.

[0006] (2) Insufficient microstructure and overall durability. In Chinese authorized patent CN106242338B, the acid-base lithium slag is simply physically mixed. The activity of lithium slag pozzolanic remains low in the early stage, and the residual sulfate in the early acid process lithium slag can interfere with cement hydration. Under high admixture, the early strength and later density of concrete are both poor. Existing technologies also do not address the problem of weakening of the interface transition zone when lithium slag is used as a high proportion admixture.

[0007] (3) Environmental safety hazards have not been resolved. Lithium smelting slag contains heavy metal elements such as Be (beryllium), Tl (thallium), and Mn (manganese), which have a high leaching risk under certain conditions. In particular, the calcium introduced into the alkaline lithium slag can promote the release of heavy metal ions from the solid phase through ion exchange, further increasing the leaching risk.

[0008] The aforementioned deficiencies in existing lithium slag application technologies in the concrete field make it difficult to meet the demands of higher lithium slag content and wider application scenarios in concrete, given the current explosive growth of lithium battery solid waste. Systematic optimization is needed to construct a lithium slag building material utilization technology system that is oriented towards high content, excellent performance, and environmental safety, and to promote the leap from "low-value disposal" to "high-value utilization" of lithium smelting slag. Summary of the Invention

[0009] This invention provides a lithium slag powder-based multi-component solid waste low-carbon concrete and its preparation method. This invention utilizes an acid-base lithium slag gradient mineralization core-shell structure design and the synergistic effect of multiple components in the concrete formulation system. By modifying lithium slag powder, optimizing the rheological properties of concrete, and controlling the microstructure of cement-based materials, it addresses technical shortcomings such as low stability of acid-base-lithium slag co-processing and poor performance of high-content lithium slag concrete. This improves the working and mechanical properties and environmental safety of lithium slag powder-based multi-component solid waste concrete, achieving efficient and high-value utilization of bulk solid waste. Specifically, this invention is achieved through the following technologies.

[0010] This invention provides a lithium slag powder-based multi-element solid waste low-carbon concrete, comprising, by weight parts: 150-170 parts cement, 40-50 parts fly ash, 130-150 parts lithium slag powder, 820-860 parts iron tailings sand, 200-250 parts recycled aggregate, 800-850 parts limestone crushed stone, 7-10 parts water-reducing agent, 155-165 parts water, 0.6-1.0 parts humic acid, and 0.5-1 parts hydroxypropyl guar gum.

[0011] The method for preparing the lithium slag powder includes: The core microspheres are obtained by wet milling and activation of 70-85 parts by weight of acid process lithium slag, 2-5 parts by weight of biochar and 0.5-1 parts by weight of polyethylene glycol, followed by drying and granulation.

[0012] Pour 1.5-2.5 parts by weight of VAE emulsion into 0.5-1 parts of nano-silica aqueous dispersion, stir evenly, add a total of 10-20 parts of alkaline lithium slag in batches, stir evenly, adjust the solid content and viscosity of the system to obtain shell slurry.

[0013] The shell slurry is coated on the surface of the core microspheres and dried to obtain the core-shell type lithium slag powder.

[0014] In the existing technology, simply mixing acid process lithium slag and alkali process lithium slag and then adding them directly to concrete will cause the acid and alkali lithium slag, residual acid, and Ca(OH)2 to come into disorderly contact at the same time. This can easily lead to localized severe but uneven acid-alkali neutralization of lithium slag powder, resulting in problems such as flash setting, low filling rate of porous structure, and powder agglomeration in concrete.

[0015] The lithium slag powder-based multi-element solid waste low-carbon concrete provided by this invention is based on an acid-alkali lithium slag gradient mineralization core-shell structure design. It fully leverages and avoids the respective advantages and disadvantages of acid-process lithium slag (higher amorphous SiO2 / Al2O3 ratio, more porous, and more layered structure) and alkaline-process lithium slag (relatively higher Ca(OH)2, more efficient early-stage volcanic ash reaction), spatially separating the two at the micrometer scale to achieve synergistic effects and compensate for each other's weaknesses. Specifically, this invention utilizes the synergistic mechanism of polymer "alkali hydrolysis response," alkaline-process lithium slag "targeted calcium supply," and acid-process lithium slag "high activity in the later stages" to achieve a gradual gradient reaction of "alkali first, then acid, from the surface to the interior" in the application of acid-alkali lithium slag. The shell layer of alkaline-process lithium slag provides an early local alkaline environment, gradually neutralizing the residual acid in acid-process lithium slag, avoiding instantaneous local pH changes during simple mixing that could lead to cement flashing or coarse hydration products; acid-process lithium slag, with its abundant amorphous SiO2 / Al2O3, provides activity for later secondary hydration, enhancing later strength.

[0016] When lithium slag powder is added to concrete, the VAE copolymer (ethylene-vinyl acetate copolymer) in the shell layer exhibits excellent waterproof barrier properties in the early stages of mixing. Simultaneously, the layer of alkaline lithium slag effectively isolates and neutralizes the acid-process lithium slag inside, preventing early cement hydration anomalies caused by the porous, highly absorbent nature of the acid-process lithium slag and residual acid. As cement hydration progresses, the concrete pore fluid gradually becomes strongly alkaline (pH ≥ 12.5), promoting the gradual saponification and hydrolysis of the ester groups on the VAE copolymer molecular chains (generating polyvinyl alcohol and calcium acetate), leading to directional cracking and disintegration of the polymer shell. During this process, the premixed nano-silica in the shell layer rapidly reacts with the free Ca(OH)2 released from the cement in an ultrafast pozzolanic reaction, generating high-density nano-CSH gel nuclei in situ. Simultaneously, combined with the inherent alkaline properties of the alkaline lithium slag, the lithium slag integrates well into the early hydration process of the cement, jointly strengthening the interfacial transition zone (ITZ).

[0017] With the alkaline hydrolysis of the shell and the secondary hydration of alkaline lithium slag, a localized high-calcium microenvironment is formed in the alkaline lithium slag, and Ca permeates into the core. 2+ Moisture and water promote in-situ reactions in the kernel pores, leaving residual H2SO4 and Ca. 2+ The aluminum phase hydration products react to form micro-expanded AFt, and amorphous SiO2 / Al2O3 reacts with Ca. 2+ The reaction generates CSH and CAH precipitates. Simultaneously, the biochar in the core provides nucleation sites, resulting in finer and more uniform CSH crystals, promoting the densification of the loose, porous acid-process lithium slag particles. The delayed-formation AFt and CSH gels, to some extent, counteract the auto-shrinkage of the concrete during the cooling and hardening periods.

[0018] Biochar adsorbs SO4 from acid-process lithium slag during the wet milling activation stage. 2- In the later stage, it provides a large number of heterogeneous nucleation sites for CSH, and at the same time fixes heavy metal ions through cation exchange, complexation and pore adsorption; while the hydration products of lithium slag powder can further encapsulate the heavy metals adsorbed on biochar, forming a "triple fixation" of adsorption, hydration encapsulation and mineral phase stabilization.

[0019] Polyethylene glycol (PEG) plays a role in dispersion and grinding aid during wet grinding. The residual PEG molecular chains are adsorbed on the surface of acid process lithium slag through hydrogen bonds. Its side chains provide steric hindrance, which plays a lubricating role and reduces the water requirement of lithium slag.

[0020] VAE (ethylene-vinyl acetate copolymer) is a flexible polymer, while nano-silica is a rigid inorganic nanoparticle. It can be uniformly dispersed and embedded within the VAE polymer network. The numerous hydroxyl groups on the SiO2 surface undergo hydrogen bonding cross-linking with the polar groups of VAE, improving the mechanical strength and wear resistance of the film. VAE undergoes alkaline hydrolysis and reacts with Ca in cementitious materials. 2+ The generated calcium acetate has an early strength effect, accelerates the hydration of C3S in cement, and enhances the early strength of high-volume lithium slag concrete; the generated polyvinyl alcohol (PVA) long chain forms a strong and tough three-dimensional hydrogen bond network with hydroxypropyl guar gum (HPG) in concrete through a large number of hydroxyl groups, which improves the water retention and anti-bleeding performance of cement-based paste.

[0021] Recycled aggregates are characterized by high porosity, high water absorption, and a weak interfacial transition zone. After pre-wetting treatment, they can act as uniformly dispersed "micro-reservoirs" in concrete mixtures. In the later stages of hydration, acid-process lithium slag undergoes a secondary hydration reaction, consuming the water within the surrounding slurry and causing a decrease in local relative humidity. The resulting water potential difference causes the pre-wetted water stored inside the recycled aggregates to be gradually "drawn out," providing additional water for the secondary hydration of lithium slag and enhancing later-stage strength. At the same time, the lithium slag-cement secondary hydration product (CSH gel) can fill the old pores and micro-cracks on the surface of the recycled aggregates through capillary water migration channels, improving the interfacial transition zone of the recycled aggregates.

[0022] In the lithium slag powder-based multi-element solid waste low-carbon concrete provided by this invention, fulvic acid (FA) provides a "dispersion + chelation + surface activity" effect, improving workability and later strength while reducing the risk of heavy metals. Specifically, the fulvic acid molecular skeleton has a dense distribution of highly active carboxyl groups (-COOH) and phenolic hydroxyl groups (-Ar-OH), exhibiting strong anionic surface activity and chelation ability. When added to concrete, it can be adsorbed on the surface of cement, lithium slag, and other powders, generating electrostatic repulsion and steric hindrance, thus improving the fluidity of the slurry. When trace heavy metal ions are free in the liquid phase pores of the concrete, the oxygen atoms on the FA molecular chain will provide lone pairs of electrons to the empty orbitals of the heavy metals, forming negatively charged five-membered or six-membered ring "chelates," while simultaneously adsorbing positively charged hydration products, effectively solidifying the trace heavy metals released from lithium slag and iron tailings, and reducing the risk of leaching.

[0023] Furthermore, in the preparation method of the lithium slag powder, the wet milling activation conditions are: water-to-solid ratio of 0.3-0.4, wet milling ball-to-material ratio of 10:1, and treatment for 30-60 min; the particle size of the core microspheres is 40-150 μm.

[0024] Furthermore, the core-shell type lithium slag powder has a particle size of 50-200 μm, and the coating thickness formed by the shell slurry is 10-30 μm.

[0025] Furthermore, the acid-process lithium slag is a byproduct of lithium extraction from spodumene using the sulfuric acid process, and its chemical composition, by mass fraction, includes 50-60% SiO2, 20-25% Al2O3, 4-6% CaO, 6-10% SO3, and 1-3% residual H2SO4; the specific surface area of ​​the acid-process lithium slag is 2.0-3.5 m². 2 / g; Particle size distribution D 50 =15-30 μm.

[0026] Furthermore, the alkaline lithium slag is a byproduct of lithium extraction from lepidolite using the sulfate / sodium carbonate method, and its chemical composition by mass fraction includes SiO2 38-47%, Al2O3 16-21%, CaO 17-22%, SO3 4-7%, and Ca(OH)2 2.5-4.0%; the specific surface area of ​​the alkaline lithium slag is 1.5-2.5 m². 2 / g; Particle size distribution D 50 =10-20 μm.

[0027] Furthermore, the preparation method of the hydroxypropyl guar gum includes: Natural guar gum powder is dispersed in an aqueous ethanol solution, and then alkali solution is added for alkalization treatment.

[0028] After adding propylene oxide, the mixture was heated in a closed environment to react. After cooling to room temperature, the pH was adjusted to neutral, and the mixture was washed and dried to obtain the hydroxypropyl guar gum.

[0029] Hydroxypropyl guar gum (HPG) can effectively solve the problems of bleeding, segregation, and workability loss caused by high solid waste systems. Natural guar gum has strong intermolecular hydrogen bonds, poor solubility in cold water, and high insoluble matter content. In the highly alkaline environment of cement, it easily agglomerates, leading to uneven slurry and reduced strength. Hydroxypropyl modification utilizes the etherification reaction between natural guar gum and propylene oxide to increase steric hindrance, making the molecular chains more extended. When added to concrete, the long chains of galactomannan dissolve in water to form an entangled polymer network. This network adsorbs onto the surface of cement particles, lithium slag powder, and iron tailings sand through hydrogen bonds and van der Waals forces, forming a "colloidal bridging" structure. This increases the plastic viscosity of the slurry, inhibits the sedimentation of solid particles (especially iron tailings sand with large density differences), and prevents bleeding. The hydroxyl groups of hydroxypropyl guar gum can interact with the CSH gel surface, delaying the early hydration peak, reducing free water evaporation, maintaining the humidity required for hydration, and promoting later pozzolanic reactions. Hydroxypropyl guar gum also works synergistically with fulvic acid for stabilization. The carboxyl and phenolic hydroxyl groups of FA can form hydrogen bonds and weak complexes with the hydroxyl groups of HPG. FA acts as a "crosslinking point," enhancing the stability of the HPG colloidal network and making the polymer chains less prone to breakage. At the same time, FA can reduce the adsorption competition of HPG, allowing more HPG to remain in the liquid phase and play a water-retaining role.

[0030] Furthermore, the amount of propylene oxide used is 10%-30% of the mass of natural guar gum powder.

[0031] Furthermore, the alkalization treatment conditions are: room temperature treatment for 15-30 min.

[0032] Furthermore, the reaction conditions after adding propylene oxide are: approximately 65-75℃ for 1.5-3 hours.

[0033] This invention also provides a method for preparing low-carbon concrete based on lithium slag powder using the above-mentioned lithium slag powder, comprising the following steps: Fulvic acid, hydroxypropyl guar gum, and water-reducing agent are added to water accounting for 30%-40% of the total water volume and dispersed evenly to obtain a composite admixture.

[0034] Iron tailings sand, recycled aggregate, and limestone crushed stone are mixed together, and then cement, fly ash, and lithium slag powder are added and mixed further to obtain a mixture.

[0035] The composite admixture and the remaining water are added to the mixture and mixed evenly to obtain concrete slurry.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] 1. This invention constructs a gradient mineralization core-shell structure of "acid process lithium slag core - alkali process lithium slag shell" to achieve spatial separation and staged reaction of acid and alkali lithium slag at the micron scale, avoiding the problems of localized violent neutralization, flash coagulation, agglomeration and pore structure defects caused by instantaneous contact after simple mixing of acid and alkali lithium slag in the prior art.

[0038] The shell layer of alkaline lithium slag can preferentially provide a localized alkaline environment and gradually neutralize the residual acid in acid-process lithium slag, while the VAE polymer shell layer forms a barrier protection in the early stage. As the alkalinity of the cement-based material increases, the shell layer undergoes alkaline hydrolysis and rupture, prompting the acid-process lithium slag to continuously participate in the secondary hydration reaction in the later stage, realizing a gradual reaction process of "alkaline first, then acid, from the surface to the inside".

[0039] This special lithium slag powder core-shell structure not only improves the working stability and interfacial density of high-volume lithium slag concrete, but also enhances the later-stage strength development, realizing the synergistic utilization of acid-process lithium slag and alkaline-process lithium slag.

[0040] 2. This invention establishes a composite regulation system with "water retention-thickening-dispersion-interface strengthening" functions through the synergistic effect between fulvic acid, hydroxypropyl guar gum (HPG), VAE alkaline hydrolysis products and nano-SiO2, effectively solving the problems of fluidity loss, bleeding segregation and weak interface that are prone to occur in concrete with high solid waste and high lithium slag content.

[0041] HPG enhances the plastic viscosity of the slurry and inhibits aggregate settling by forming a polymer entanglement network; fulvic acid improves slurry flowability through electrostatic dispersion and complexation. Polyvinyl alcohol (PVA) generated from the alkaline hydrolysis of VAE further forms a three-dimensional hydrogen bond network with HPG, improving the slurry's water retention and anti-bleeding properties. Nano-SiO2 promotes early in-situ CSH gel formation and strengthens the interfacial transition zone. Simultaneously, the "internal curing" effect of recycled aggregates sustainably releases stored moisture, providing a water source for the later-stage volcanic ash reaction of lithium slag and reducing the risk of autogenous shrinkage.

[0042] 3. This invention fully utilizes various industrial solid wastes such as acid-process lithium slag, alkaline-process lithium slag, iron tailings sand, and recycled aggregates, improving the utilization rate of solid waste while also considering environmental safety and engineering application reliability, demonstrating significant low-carbon and environmentally friendly benefits. Through a triple fixation mechanism of "biochar adsorption - hydration product encapsulation - mineral phase stabilization," heavy metal ions in lithium slag and iron tailings are synergistically solidified. Specifically, biochar can adsorb SO4. 2- It also provides heterogeneous nucleation sites for heavy metal ions; humic acid stabilizes heavy metals through carboxyl and phenolic hydroxyl groups; the CSH gel and AFt crystals generated later further encapsulate and fix the heavy metals, thereby effectively reducing the risk of heavy metal leaching. Detailed Implementation

[0043] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] This invention provides a lithium slag powder-based multi-element solid waste low-carbon concrete, comprising, by weight parts: 150-170 parts cement, 40-50 parts fly ash, 130-150 parts lithium slag powder, 820-860 parts iron tailings sand, 200-250 parts recycled aggregate, 800-850 parts limestone crushed stone, 7-10 parts water-reducing agent, 155-165 parts water, 0.6-1.0 parts humic acid, and 0.5-1 parts hydroxypropyl guar gum.

[0045] The preparation methods for lithium slag powder include: The core microspheres are obtained by wet milling and activation of 70-85 parts by weight of acid process lithium slag, 2-5 parts by weight of biochar and 0.5-1 parts by weight of polyethylene glycol, followed by drying and granulation.

[0046] Slowly pour 1.5-2.5 parts by weight of VAE emulsion into 0.5-1 parts of nano-silica aqueous dispersion, stir evenly, and add a total of 10-20 parts of alkaline lithium slag in batches (e.g., 3-4 batches), stir evenly, adjust the solid content and viscosity of the slurry system to obtain the shell slurry.

[0047] The shell slurry is coated on the surface of the core microspheres and dried to obtain the core-shell type lithium slag powder.

[0048] Optionally, in the above-mentioned method for preparing lithium slag powder, the acid-process lithium slag and the alkaline-process lithium slag are dried to constant weight in an oven at 105°C before use.

[0049] Optionally, in the above-mentioned method for preparing lithium slag powder, the wet milling activation conditions are: a water-to-solid ratio of 0.3-0.4, grinding balls made of zirconia with a diameter of 6-10 mm, a wet milling speed of 250-350 rpm, a wet milling ball-to-material ratio of 10:1, and a treatment time of 30-60 min. In the following specific embodiment, the water-to-solid ratio for wet milling activation is 0.35, the grinding balls are made of zirconia with a diameter of approximately 8 mm, the wet milling speed is 300 rpm, the wet milling ball-to-material ratio is 10:1, and the treatment time is 45 min.

[0050] Optionally, wet milling activation can be performed in a planetary ball mill. Drying and granulation can be carried out in a spray dryer (e.g., inlet temperature 160-220℃, outlet temperature 80-110℃, atomization pressure 0.2-0.4 MPa). The final core microspheres have a particle size of 40-150 μm. In the following specific embodiments, the operating parameters of the spray dryer are: inlet temperature 200℃, outlet temperature 95℃, atomization pressure 0.3 MPa, and the final core microspheres have a particle size of 60-100 μm.

[0051] Optionally, the final shell slurry typically has a solid content of 20-24%, and the solid content and viscosity are adjusted with deionized water to a viscosity of 180-260 mPa‧s (25°C, Brookfield, 10 rpm). In the following specific embodiments, the solid content of the shell slurry is typically controlled to be 20-22%, and the viscosity to be 200-220 mPa‧s (25°C, Brookfield, 10 rpm).

[0052] Optionally, the "coating" process of applying the shell slurry to the surface of the core microspheres can be carried out in an industrial fluidized bed coating machine. Specifically, the core microspheres are placed in a fluidized bed, and the shell slurry is atomized and sprayed onto the surface of the fluidized core particles through a spray gun, and then dried with hot air. This spray-dry cycle is repeated until the required coating thickness is met.

[0053] The final core-shell type lithium slag powder has a particle size of 50-200 μm, and the coating thickness formed by the shell slurry is 10-30 μm. In the following specific embodiments, the core-shell type lithium slag powder has a particle size of 100-150 μm, and the coating thickness formed by the shell slurry is 10-20 μm.

[0054] Optionally, the acid-process lithium slag used in the preparation of lithium slag powder is a byproduct of lithium extraction from spodumene using the sulfuric acid process. Its chemical composition, by mass fraction, includes 50-60% SiO2, 20-25% Al2O3, 4-6% CaO, 6-10% SO3, and 1-3% residual H2SO4; the remainder being trace impurities. The specific surface area of ​​the acid-process lithium slag is 2.0-3.5 m². 2 / g; Particle size distribution D50 =15-30 μm.

[0055] Optionally, the alkaline lithium slag used in the preparation of lithium slag powder is a byproduct of lithium extraction from lepidolite using the sulfate / sodium carbonate method. Its chemical composition, by mass fraction, includes SiO2 38-47%, Al2O3 16-21%, CaO 17-22%, SO3 4-7%, Ca(OH)2 2.5-4.0%; the remainder being Na2O, K2O, etc. The specific surface area of ​​the alkaline lithium slag is 1.5-2.5 m². 2 / g; Particle size distribution D 50 =10-20 μm.

[0056] Methods for preparing hydroxypropyl guar gum include: Natural guar gum powder is dispersed in an aqueous ethanol solution, and then alkali solution is added for alkalization treatment.

[0057] After adding propylene oxide and heating to react, the mixture was cooled to room temperature and the pH was adjusted to neutral. The mixture was then washed and dried to obtain hydroxypropyl guar gum.

[0058] The main component of natural guar gum powder is galactomannan.

[0059] Optionally, a 5-30 wt% NaOH solution is typically used as the catalyst for the alkalization treatment.

[0060] Optionally, when preparing hydroxypropyl guar gum, the amount of propylene oxide used is 10%-30% of the mass of natural guar gum powder.

[0061] Optionally, when preparing hydroxypropyl guar gum, the alkalization treatment conditions are: room temperature treatment for 15-30 min.

[0062] Optionally, when preparing hydroxypropyl guar gum, the reaction conditions after adding propylene oxide and heating are: approximately 65-75℃ for 1.5-3 h.

[0063] Optionally, acetic acid is generally used to neutralize the pH value until the pH value is approximately 7.0; then unreacted substances are washed away with ethanol and vacuum dried to obtain hydroxypropyl guar gum powder.

[0064] In the following specific implementation examples, the preparation method of hydroxypropyl guar gum is as follows: (1) Disperse natural guar gum powder in an ethanol-water mixed solvent (ethanol volume fraction of 60%-85%) to form a suspension; the mass ratio of the mixed solvent to natural guar gum powder is (4-10):1.

[0065] Then, a sodium hydroxide solution (mass fraction of 20%-40%) is added, the amount of sodium hydroxide being 3%-15% of the mass of the natural guar gum powder, and the mixture is mechanically stirred at room temperature for 15-30 minutes for alkalization and swelling.

[0066] (2) Place the system in a closed reactor, add propylene oxide of 10%-30% of natural guar gum powder, heat to 65-75℃ under 0.05-0.3 MPa pressure and stir continuously for 1.5-3 h to carry out etherification reaction.

[0067] (3) After the reaction is completed, cool to room temperature, adjust the pH of the system to 6.5-7.5 with glacial acetic acid, wash with ethanol, filter, and then vacuum dry at 50-70℃ for 6-12 h to obtain hydroxypropyl guar gum.

[0068] In some embodiments of the present invention, the method for preparing lithium slag powder-based multi-element solid waste low-carbon concrete is as follows: (1) Add fulvic acid, hydroxypropyl guar gum and water-reducing agent to 30%-40% of the total water (about 50-65 parts of water), and stir for 4-6 minutes using a high-speed disperser (600-800 r / min) until a uniform, low-viscosity composite additive solution is formed.

[0069] (2) Add iron tailings sand, recycled aggregate and limestone crushed stone into a forced mixer and dry mix at low speed for 1-2 minutes. Then add cement, fly ash and lithium slag powder and continue to dry mix for 2-3 minutes until the powder evenly covers the surface of the aggregate and there is no obvious color difference, thus obtaining the mixture.

[0070] (3) Add the remaining water and the composite admixture solution slowly to the mixer and stir for 3-4 minutes until the mixture is uniformly mixed to obtain lithium slag powder-based multi-element solid waste low-carbon concrete slurry.

[0071] In the following specific implementation cases, the sources and specifications of the main raw materials for preparing lithium slag powder, hydroxypropyl guar gum, and concrete are shown in Table 1 below.

[0072] Table 1

[0073]

[0074] Example 1

[0075] The lithium slag powder-based multi-element solid waste low-carbon concrete provided in this embodiment includes, by weight parts: 160 parts cement, 45 parts fly ash, 140 parts lithium slag powder, 840 parts iron tailings sand, 225 parts recycled aggregate, 825 parts limestone crushed stone, 8 parts water-reducing agent, 160 parts water, 0.8 parts humic acid, and 0.7 parts hydroxypropyl guar gum.

[0076] The raw materials for lithium slag powder, by mass, include: 79 parts of acid process lithium slag, 15 parts of alkali process lithium slag, 3.5 parts of biochar, 0.75 parts of polyethylene glycol (PEG), 2 parts of VAE emulsion, and 0.75 parts of nano silica aqueous dispersion.

[0077] The method for preparing lithium slag powder used in this embodiment is as follows:

[0078] (1) Dry the acid process lithium slag and the alkaline process lithium slag in an oven at 105°C until constant weight.

[0079] Acid-process lithium slag, biochar, and polyethylene glycol were added to a planetary ball mill for wet milling and activation, followed by drying and granulation to obtain core microspheres.

[0080] (2) Slowly pour the VAE emulsion into the nano silica aqueous dispersion and stir at low speed at room temperature (200 r / min, 15 min). Add the alkaline lithium slag in 3-4 batches and stir evenly (300 r / min, 30 min). Adjust the solid content and viscosity of the slurry with deionized water to obtain the shell slurry.

[0081] (3) Using an industrial fluidized bed coating machine, core microspheres are placed in a fluidized bed; shell slurry is atomized and sprayed onto the surface of fluidized core particles through a spray gun, dried with hot air, and repeatedly sprayed-dried until the core-shell type lithium slag powder is obtained.

[0082] The preparation method of hydroxypropyl guar gum used in this embodiment is as follows:

[0083] (1) Disperse natural guar gum powder in an ethanol-water mixed solvent to form a suspension, wherein the volume fraction of ethanol is 72% and the mass ratio of the mixed solvent to natural guar gum powder is 7:1; then add a sodium hydroxide solution with a mass fraction of 30%, wherein the amount of sodium hydroxide is 9% of the mass of natural guar gum powder, and perform alkalization and swelling treatment at room temperature by mechanical stirring for 25 min.

[0084] (2) Place the system in a closed reactor, add propylene oxide of 20% of the mass of natural guar gum powder, heat to 80°C under a pressure of 0.1-0.2 MPa and stir continuously for 2.5 h to carry out the etherification reaction.

[0085] (3) After the reaction was completed, the system was cooled to room temperature, and the pH of the system was adjusted to 7-7.5 with glacial acetic acid. After washing with ethanol and filtering, the system was vacuum dried at 60°C for 9 h to obtain hydroxypropyl guar gum.

[0086] The preparation method of lithium slag powder-based multi-element solid waste low-carbon concrete in this embodiment is as follows:

[0087] (1) Add fulvic acid, hydroxypropyl guar gum and water-reducing agent to water with a total volume of 35%, and stir for 5 minutes using a high-speed disperser (700r / min) until a uniform, low-viscosity composite additive solution is formed.

[0088] (2) Add iron tailings sand, recycled aggregate and limestone crushed stone to a forced mixer and dry mix at low speed for 1 min. Then add cement, fly ash and lithium slag powder and continue to dry mix for 3 min until the powder evenly coats the surface of the aggregate and there is no obvious color difference, thus obtaining the mixture.

[0089] (3) Add the remaining water and the composite admixture solution slowly to the mixer and stir for 3 minutes until the mixture is evenly mixed to obtain lithium slag powder-based multi-element solid waste low-carbon concrete slurry.

[0090] Example 2

[0091] The lithium slag powder-based multi-element solid waste low-carbon concrete provided in this embodiment includes, by weight parts: 150 parts cement, 40 parts fly ash, 150 parts lithium slag powder, 860 parts iron tailings sand, 250 parts recycled aggregate, 800 parts limestone crushed stone, 7 parts water-reducing agent, 155 parts water, 1.0 part humic acid, and 1.0 part hydroxypropyl guar gum.

[0092] The preparation methods for lithium slag powder and hydroxypropyl guar gum, as well as the preparation method for concrete, are the same as in Example 1.

[0093] Example 3

[0094] The lithium slag powder-based multi-element solid waste low-carbon concrete provided in this embodiment includes, by weight, the following components: 170 parts cement, 50 parts fly ash, 130 parts lithium slag powder, 820 parts iron tailings sand, 200 parts recycled aggregate, 850 parts limestone crushed stone, 10 parts water-reducing agent, 165 parts water, 0.6 parts humic acid, and 0.5 parts hydroxypropyl guar gum.

[0095] The preparation methods for lithium slag powder and hydroxypropyl guar gum, as well as the preparation method for concrete, are the same as in Example 1.

[0096] Example 4

[0097] The lithium slag powder-based multi-element solid waste low-carbon concrete provided in this embodiment differs from that in Example 1 in that the raw materials of the lithium slag powder include, by mass, 70 parts of acid process lithium slag, 10 parts of alkali process lithium slag, 2 parts of biochar, 0.5 parts of polyethylene glycol (PEG), 1.5 parts of VAE emulsion, and 0.5 parts of nano silica aqueous dispersion.

[0098] The preparation methods for lithium slag powder and hydroxypropyl guar gum, as well as the raw material dosage and preparation method for concrete, are the same as in Example 1.

[0099] Example 5

[0100] The lithium slag powder-based multi-element solid waste low-carbon concrete provided in this embodiment differs from that in Example 1 in that the raw materials of the lithium slag powder include, by mass, 85 parts of acid process lithium slag, 20 parts of alkali process lithium slag, 5 parts of biochar, 1 part of polyethylene glycol (PEG), 2.5 parts of VAE emulsion, and 1 part of nano silica aqueous dispersion.

[0101] The preparation methods for lithium slag powder and hydroxypropyl guar gum, as well as the raw material dosage and preparation method for concrete, are the same as in Example 1.

[0102] Comparative Example 1

[0103] The difference between the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in this comparative example and Example 1 is that the lithium slag powder used in this comparative example is prepared by directly blending acid-process lithium slag and alkaline-process lithium slag. Specifically, the preparation method is as follows: based on the mass percentage of the lithium slag powder, the content of acid-process lithium slag is 85%, and the content of alkaline-process lithium slag is 15%. After weighing the raw materials according to the proportions, the acid-process and alkaline-process materials are mixed, dried at 150°C, and then ground to a specific surface area of ​​500 m². 2 / kg yields lithium slag powder.

[0104] Comparative Example 2

[0105] The difference between the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in this comparative example and Example 1 is that the lithium slag powder used in this comparative example adopts a reverse core-shell structure (i.e., the core is alkaline lithium slag and the shell is acidic lithium slag), while the composition and dosage of other lithium slag powder and concrete formula are exactly the same.

[0106] The raw materials for lithium slag powder, by mass, include: 79 parts of acid process lithium slag, 15 parts of alkali process lithium slag, 3.5 parts of biochar, 0.75 parts of polyethylene glycol (PEG), 2 parts of VAE emulsion, and 0.75 parts of nano silica aqueous dispersion.

[0107] The lithium slag powder preparation method used in this comparative example is as follows:

[0108] (1) The lithium slag from the acid-base method was dried in an oven at 105°C until constant weight.

[0109] Alkali lithium slag, biochar, and polyethylene glycol were added to a planetary ball mill for wet milling and activation, followed by drying and granulation to obtain core microspheres.

[0110] (2) Slowly pour the VAE emulsion into the nano silica aqueous dispersion and stir at low speed at room temperature (200 r / min, 15 min). Add the acid process lithium slag in 3-4 batches and stir evenly (300 r / min, 30 min). Appropriately increase the solid content and viscosity of the slurry to obtain the shell slurry.

[0111] (3) Using an industrial fluidized bed coating machine, core microspheres are placed in a fluidized bed; shell slurry is atomized and sprayed onto the surface of fluidized core particles through a spray gun, dried with hot air, and repeatedly sprayed-dried until core-shell lithium slag powder is obtained.

[0112] Comparative Example 3

[0113] The difference between the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in this comparative example and Example 1 is that, in the preparation of the lithium slag powder in this comparative example, the shell slurry is composed of alkaline lithium slag and water, and does not contain VAE emulsion and nano silica aqueous dispersion.

[0114] Comparative Example 4

[0115] The difference between the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in this comparative example and Example 1 is that, in the preparation of the lithium slag powder in this comparative example, no biochar is added to the core, and only acid-process lithium slag and polyethylene glycol are used.

[0116] Comparative Example 5

[0117] The difference between the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in this comparative example and Example 1 is that humic acid is not added to the raw materials of this comparative concrete.

[0118] Comparative Example 6

[0119] The difference between the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in this comparative example and Example 1 is that hydroxypropyl guar gum is not added to the raw materials of this comparative concrete.

[0120] Experimental Example: Performance Testing of Concrete

[0121] The workability, mechanical properties, and impermeability of the concrete prepared in the above embodiments and comparative examples were tested, and the leaching concentration of heavy metals in the fresh concrete was determined.

[0122] According to the provisions of GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the workability of fresh concrete in the examples and comparative examples was tested; the mechanical properties of concrete were tested according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete". According to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", the "permeability height method" was used to determine the average permeability height of concrete under constant water pressure, to characterize the water penetration resistance of concrete. The larger the average permeability height value of the specimen, the worse the water penetration resistance of the specimen.

[0123] Leaching was carried out according to the "Solid Waste Leaching Toxicity Leaching Method Acetic Acid Buffer Solution Method" (HJ / T 300-2007); the concentrations of Be, Tl and Mn ions in the leachate were determined by ICP-OES.

[0124] The performance test results of each type of concrete are shown in Table 2, and the heavy metal leaching concentration test results are shown in Table 3.

[0125] Table 2 Test Results of Concrete Performance

[0126]

[0127] As can be seen from the test results in Table 2, the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in the embodiments of the present invention all have excellent workability, compressive strength and density.

[0128] In Examples 1-5, the initial slump of the concrete remained between 210-220 mm, with minimal slump loss over 2 hours. The slurry exhibited excellent cohesiveness, with no significant segregation or bleeding. This indicates that the present invention, through its gradient mineralization core-shell structure design of "acid-process lithium slag core - alkali-process lithium slag shell" and the synergistic effect of multiple components such as humic acid, hydroxypropyl guar gum, VAE, and nano-silica, can effectively improve the working stability of the high-content lithium slag system. Among these, Example 3 exhibited the highest 28-day compressive strength (40.6 MPa) and the lowest water seepage height (only 24 mm), demonstrating that appropriately increasing the dosage of cement and water-reducing agent while reducing the lithium slag content is beneficial for improving the system's density and impermeability.

[0129] In contrast, in Comparative Example 1, the direct blending of acid-process and alkali-process lithium slag resulted in drastic local pH changes and particle agglomeration due to the instantaneous contact between the acid and alkali lithium slags. This caused the initial slump of the concrete to plummet to 180 mm, with a 2-hour loss of up to 75 mm, and localized flash setting also occurred. Simultaneously, the disordered reaction led to a loose microstructure, significantly deteriorating both mechanical and impermeability properties. The 28-day compressive strength decreased to 31.2 MPa, and the water seepage height increased to 44 mm. This demonstrates that the core-shell structure constructed in this invention can effectively avoid the adverse effects of disordered contact between acid and alkali lithium slags.

[0130] Comparative Example 2, employing an "alkali core-acid shell" structure, also showed significantly lower concrete performance compared to Example 1. A large amount of acid-process lithium slag was on the outer layer, which not only prematurely absorbed moisture, leading to increased slump loss (45 mm), but more importantly, consumed the early alkalinity of the system, inhibiting cement hydration. Meanwhile, the core alkali-process lithium slag was encapsulated, unable to exert its early activation advantage of "targeted calcium supply." The "acid core-alkali shell" structure is more conducive to achieving a gradual reaction process of "alkali first, then acid, from the surface to the interior."

[0131] In Comparative Example 3, due to the absence of VAE emulsion and nano-silica in the shell layer, and the lack of early waterproofing barrier effect from the polymer film, moisture prematurely penetrated into the acid-process core, resulting in poorer initial slump and 2-hour slump loss. Furthermore, the absence of polyvinyl alcohol (PVA) generated from VAE alkaline hydrolysis to form a three-dimensional hydrogen bond network with HPG led to slight bleeding in the slurry. In addition, the lack of in-situ reaction between nano-SiO2 and VAE alkaline hydrolysis products resulted in the absence of high-density CSH crystal nuclei filling the interfacial transition zone (ITZ), leading to a decrease in compressive strength (34.8 MPa) and reduced density.

[0132] In Comparative Example 4, the compressive strength and impermeability of concrete decreased slightly after the removal of biochar. This was mainly because the core of the acid process lithium slag lacked heterogeneous nucleation sites, resulting in uneven distribution of secondary hydration products (such as CSH) and insufficient densification. Ultimately, this led to a slight deterioration in the 28-day compressive strength (36.2 MPa) and the density of the system.

[0133] In Comparative Example 5, since no fulvic acid was added, the high-dosage solid waste system lost the electrostatic repulsion and steric hindrance effect of FA, the initial fluidity of the system decreased (slump 200 mm), the slurry was slightly dry, and the concrete mechanics and density were also slightly deteriorated due to the poor workability.

[0134] In Comparative Example 6, without the addition of hydroxypropyl guar gum, although the initial slump value did not change much, the concrete mixture exhibited bleeding and aggregate settling. Bleeding and segregation directly led to uneven internal structure of the hardened concrete, resulting in a decrease in mechanical and impermeability properties. This indicates that the polymer network structure formed by hydroxypropyl guar gum plays an important role in maintaining slurry stability, inhibiting segregation and bleeding, and improving pore structure.

[0135] Table 3. Test results of heavy metal leaching concentration in concrete

[0136]

[0137] As can be seen from the results in Table 3, the leaching concentrations of heavy metal ions such as Be, Tl, and Mn in the lithium slag powder-based multi-element solid waste low-carbon concrete prepared in the embodiments of the present invention are maintained at a low level. This indicates that the present invention can achieve stable solidification of heavy metal ions through the synergistic effects of acid-base lithium slag gradient mineralization core-shell structure design, biochar adsorption, fulvic acid complexation, and encapsulation of subsequent hydration products.

[0138] In Comparative Example 1, due to the direct blending of acid-process lithium slag and alkaline-process lithium slag, localized loose regions and non-uniform hydration structures easily formed within the system, leading to easier outward migration of heavy metal ions. The leaching concentrations of Be, Tl, and Mn were significantly higher than in the Example 2. In Comparative Example 2, the heavy metal leaching concentration also increased significantly after adopting a reverse core-shell structure, indicating that the "acid core-alkali shell" structure is more conducive to forming a stable and dense hydration encapsulation system, thereby inhibiting heavy metal migration to some extent. In Comparative Example 4, the leaching concentrations of Be, Tl, and Mn increased significantly due to the absence of biochar, indicating that biochar, with its rich pore structure and surface functional group complexation, can effectively physically adsorb and fix heavy metal ions within the pores. In Comparative Example 5, the lack of carboxyl and phenolic hydroxyl complexation in fulvic acid reduced the heavy metal stabilization effect, resulting in a slight increase in leaching concentration. In Comparative Example 6, the lack of hydroxypropyl guar gum reduced slurry stability, and the inhomogeneity of the macrostructure led to the formation of numerous interconnected water-secreting channels, which also increased the risk of heavy metal ion migration to some extent.

[0139] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A lithium slag powder-based multi-element solid waste low-carbon concrete, characterized in that, The composition by weight is as follows: 150-170 parts cement, 40-50 parts fly ash, 130-150 parts lithium slag powder, 820-860 parts iron tailings sand, 200-250 parts recycled aggregate, 800-850 parts limestone crushed stone, 7-10 parts water-reducing agent, 155-165 parts water, 0.6-1.0 parts humic acid, and 0.5-1 parts hydroxypropyl guar gum. The method for preparing the lithium slag powder includes: The following steps are performed by wet milling and activation: 70-85 parts by weight of acid process lithium slag, 2-5 parts by weight of biochar and 0.5-1 parts by weight of polyethylene glycol, followed by drying and granulation to obtain core microspheres. Pour 1.5-2.5 parts by weight of VAE emulsion into 0.5-1 parts of nano-silica aqueous dispersion, stir evenly, add a total of 10-20 parts of alkaline lithium slag in batches, stir evenly, adjust the solid content and viscosity of the system to obtain shell slurry. The shell slurry is coated on the surface of the core microspheres and dried to obtain the core-shell type lithium slag powder.

2. The lithium slag powder-based multi-solid waste low-carbon concrete according to claim 1, characterized in that, In the preparation method of the lithium slag powder, the wet milling activation conditions are: water-to-solid ratio of 0.3-0.4, wet milling ball-to-material ratio of 10:1, and treatment for 30-60 min; the particle size of the core microspheres is 40-150 μm.

3. The lithium slag powder-based multi-solid waste low-carbon concrete according to claim 1, characterized in that, The core-shell type lithium slag powder has a particle size of 50-200 μm, and the coating thickness formed by the shell slurry is 10-30 μm.

4. The lithium slag powder-based multi-element solid waste low-carbon concrete according to claim 1, characterized in that, The acid-process lithium slag is a byproduct of lithium extraction from spodumene using the sulfuric acid process. Its chemical composition, by mass fraction, includes 50-60% SiO2, 20-25% Al2O3, 4-6% CaO, 6-10% SO3, and 1-3% residual H2SO4. The specific surface area of ​​the acid-process lithium slag is 2.0-3.5 m². 2 / g; Particle size distribution D 50 =15-30 μm.

5. The lithium slag powder-based multi-solid waste low-carbon concrete according to claim 1, characterized in that, The alkaline lithium slag is a byproduct of lithium extraction from lepidolite using the sulfate / sodium carbonate method. Its chemical composition, by mass fraction, includes SiO2 38-47%, Al2O3 16-21%, CaO 17-22%, SO3 4-7%, and Ca(OH)2 2.5-4.0%. The specific surface area of ​​the alkaline lithium slag is 1.5-2.5 m². 2 / g; Particle size distribution D 50 =10-20 μm.

6. The lithium slag powder-based multi-solid waste low-carbon concrete according to claim 1, characterized in that, The preparation method of the hydroxypropyl guar gum includes: Natural guar gum powder is dispersed in an ethanol aqueous solution, and then alkali solution is added for alkalization treatment. After adding propylene oxide, the mixture was heated in a closed environment to react. After cooling to room temperature, the pH was adjusted to neutral, and the mixture was washed and dried to obtain the hydroxypropyl guar gum.

7. The lithium slag powder-based multi-element solid waste low-carbon concrete according to claim 6, characterized in that, The amount of propylene oxide used is 10%-30% of the mass of natural guar gum powder.

8. The lithium slag powder-based multi-element solid waste low-carbon concrete according to claim 6, characterized in that, The conditions for the alkalization treatment are: room temperature treatment for 15-30 min.

9. The lithium slag powder-based multi-element solid waste low-carbon concrete according to claim 6, characterized in that, The reaction conditions after adding propylene oxide and heating are: approximately 65-75℃ for 1.5-3 hours.

10. A method for preparing the lithium slag powder-based multi-solid waste low-carbon concrete according to any one of claims 1-9, characterized in that, Includes the following steps: Fulvic acid, hydroxypropyl guar gum, and water-reducing agent are added to water accounting for 30%-40% of the total water volume and dispersed evenly to obtain a composite admixture; Iron tailings sand, recycled aggregate, and limestone crushed stone are mixed, and cement, fly ash, and lithium slag powder are added and mixed again to obtain a mixture. The composite admixture and the remaining water are added to the mixture and mixed evenly to obtain concrete slurry.

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