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CN-122012113-A - Soil heavy metal curing composition and application method thereof

CN122012113ACN 122012113 ACN122012113 ACN 122012113ACN-122012113-A

Abstract

The invention belongs to the technical field of geotechnical engineering, in particular to the technical field of soil remediation, and particularly relates to a soil heavy metal curing composition and an application method thereof. The composition is prepared from the following raw materials of bean urease aqueous solution, chitosan aqueous solution, urea and inorganic acid, wherein the composition does not contain exogenous calcium salt. Aiming at the problems of heavy metal complex migration and secondary activation caused by high pH and the addition of exogenous calcium ions in the existing enzyme-induced carbonate precipitation (EICP) technology, the pH value of a reaction system is adjusted to 7.5-8.3 by introducing inorganic acid, and the high-efficiency solidification of heavy metals is realized under the condition of no calcium by utilizing the chelation of chitosan. The method not only avoids salinization and hardening of the soil, but also obviously reduces the bioavailability and migration risk of heavy metals, simultaneously controls the water content of the soil body, does not need subsequent dehumidification treatment, reduces engineering cost, and is particularly suitable for heavy metal pollution treatment of complex soil environments such as humus soil.

Inventors

  • CHEN YANBO
  • BIAN YI
  • ZHAN LIANGTONG
  • KE HAN
  • ZHANG YUFENG
  • Ma Borui
  • QI GUANGWEI

Assignees

  • 浙江大学

Dates

Publication Date
20260512
Application Date
20260410

Claims (10)

  1. 1. The soil heavy metal solidification composition is characterized by being prepared from the following raw materials of bean urease aqueous solution, chitosan aqueous solution, urea and inorganic acid; The soil heavy metal curing composition is prepared from the following raw materials, by mass, 100-150 parts of bean urease aqueous solution, 20-50 parts of chitosan aqueous solution, 20-40 parts of urea and 5-100 parts of inorganic acid.
  2. 2. The soil heavy metal solidifying composition according to claim 1, wherein the pH of the mixed solution of the aqueous solution of bean urease, urea and inorganic acid is controlled to 7.5-8.3.
  3. 3. The soil heavy metal solidifying composition according to claim 1, wherein the concentration of the aqueous solution of legume urease is 1-6%, the concentration of the aqueous solution of chitosan is 1-6%, and the concentration of the inorganic acid is 3-10% (w/v).
  4. 4. The soil heavy metal solidifying composition according to claim 1, wherein the inorganic acid is any one or more of sulfuric acid and hydrochloric acid.
  5. 5. The soil heavy metal solidifying composition according to claim 1, wherein the legume urease aqueous solution is 120-130 parts, the chitosan aqueous solution is 35-45 parts, the urea is 25-35 parts, and the inorganic acid is 50-60 parts.
  6. 6. The method for solidifying the heavy metal in the soil is characterized by comprising the following steps of: s100, grinding bean seeds into bean powder, and adding water to prepare bean urease aqueous solution; s200, adding urea into the bean urease aqueous solution in S100, fully stirring, reacting for 12-72 hours, and adding inorganic acid to adjust the pH of the mixed solution to obtain bean urease-urea solution; S300, dissolving chitosan powder in water to obtain a chitosan aqueous solution, uniformly mixing the chitosan aqueous solution with heavy metal contaminated soil according to a certain proportion, and standing; s400, mixing the heavy metal contaminated soil doped with chitosan in S300 and the bean urease-urea mixed solution in S200 according to a certain proportion, and standing for 12-72 hours.
  7. 7. The method according to claim 6, wherein in step S100, the bean seeds are selected from any one or more of soybean, canavalia gladiata, pigeon pea, chickpea, sword bean.
  8. 8. The method according to claim 6, wherein in step S200, the pH of the legume urease-urea solution is adjusted to a pH that is not more than 0.5 different from the pH of the heavy metal contaminated soil.
  9. 9. The method according to claim 6, wherein the standing time is 0.5 to 6 hours in step S300.
  10. 10. Use of a soil heavy metal solidifying composition according to any one of claims 1 to 5 or a method according to any one of claims 6 to 9 in the treatment of heavy metal contaminated soil.

Description

Soil heavy metal curing composition and application method thereof Technical Field The invention belongs to the technical field of geotechnical engineering, in particular to the technical field of soil remediation, and particularly relates to a soil heavy metal solidifying composition and an application method thereof. Background Along with the acceleration of the urban process and the improvement of the environmental protection requirement, a large number of simple landfill sites in China need to be excavated, screened and reused. After excavation and screening, humus soil is used as a main fine particle component, and accounts for more than 50% of the total amount of excavation garbage. The organic matter content of the humus soil exceeds 10%, the humus soil mainly comprises humus-like organic matters, lignin and the like, the water content is about 20-25%, and the pH of the soil body is 7.5-8.0. The humic soil has similar components to the fertilizer fertile soil soil, meets the requirements of GB8172-87 urban garbage agricultural control standards, has total nitrogen and total phosphorus contents of 0.41-0.76 percent and 1.02-1.18 percent respectively, is higher than that of conventional loam, has good ecological functions, and can be used as ecological restoration covering materials for slope greening, vegetation restoration and the like. However, the humus soil is seriously polluted by various heavy metals such as Cu, zn, cd, pb, and the concentration of the leaching solution generally exceeds the class III limit value of the surface water environment quality standard (GB 3838-2002). Under the action of rainfall and percolate, the heavy metal in humus soil can migrate to surrounding soil and groundwater, and ecological and water environment risks are caused. Urease-induced carbonate precipitation (Enzyme-induced carbonate precipitation, EICP) is widely used for soil heavy metal remediation as a mild, controllable biomineralization means. The technology utilizes urease to catalyze urea hydrolysis to generate carbonate ions (CO 32-) and ammonium ions (NH 4+), and the carbonate ions are combined with heavy metal ions to generate indissolvable carbonate precipitates to reduce the bioavailability of the heavy metals. In the traditional EICP technology, calcium chloride solutions with different concentrations are also introduced, calcium ions react with carbonate ions to form calcium carbonate precipitates, and heavy metals are further fixed by means of coprecipitation of calcium carbonate and heavy metal cations and adsorption complexing capacity of the calcium carbonate. However, EICP technology still faces the following technical problems that are difficult to overcome in practical applications, particularly when treating contaminated soil (e.g., humus soil) that is rich in organic matter or of a specific type: (1) After urease and urea are mixed, urea hydrolysis generates a large amount of ammonia/ammonium ions, and finally the pH value of a reaction system is quickly increased to 9.0 and above （Bian Y, Chen Y, Zhan L,et al.Effects of enzyme-induced carbonate precipitation technique on multiple heavy metals immobilization and unconfined compressive strength improvement of contaminated sand[J].Science of The Total Environment, 2024, 947(000):18.）., although alkaline environment is favorable for carbonate precipitation, for amphoteric metals (such as Cu, zn and Cd), too high pH value and high concentration of NH 4+ can induce the amphoteric metals to form soluble copper/zinc/cadmium-ammonia complex, and the complex is extremely stable and easy to migrate, so that the repairing effect is seriously weakened (CN 114605046B). In order to ensure the mineralization effect of heavy metals, the traditional EICP formula generally needs to inject a large amount of treatment fluid (the pore volume of the soil body with one time of injection amount is generally doubled) for many times, so that the moisture content of the soil body is obviously increased to be close to a saturated state, the treated soil body is in a fluid state, the engineering dehumidification cost is obviously increased, and the subsequent recycling paths of drying, screening, ecological covering material preparation and the like are not facilitated. (2) Conventional EICP techniques typically require the addition of high concentrations of exogenous calcium salts to form calcium carbonate precipitates to encapsulate heavy metal or cement particles (Science of The Total Environment, 2024, 947 (000): 18), while the addition of calcium ions is effective to alleviate the rapid rise in pH caused by urea decomposition. However, exogenous calcium ions undergo competitive ion exchange with some heavy metals (e.g., cu, zn, cd) adsorbed on the soil or organics, resulting in displacement desorption of the inherent heavy metals, rather increasing the bioavailability and migration risk of the heavy metals, and possibly resulting in soil salinization and hardenin