A method for repairing hexavalent chromium-contaminated soil and groundwater

Abstract

The invention discloses a remediation method for hexavalent chromium polluted soil and underground water. The remediation method comprises the following steps: step (10): putting a pile machine in place; step (20): independently injecting acidified bentonite slurry loaded with active carbon powder and bentonite slurry loaded with zero-valent iron powder into the ground by using stirring and injection equipment and stirring; step (30): detecting the reduction effect of hexavalent chromium in the soil and the underground water; step (40): injecting bentonite and industrial waste alkali mixed slurry; and step (50): detecting the remediation effect of hexavalent chromium and trivalent chromium. By virtue of the remediation method, remediation chemicals can be in direct and sufficient contact with the soil and the underground water to react, so that the hexavalent chromium in the soil and the underground water can be completely reduced; meanwhile, an indissolvable stable compound is formed by the trivalent chromium and the useless loss of the remediation chemicals can be reduced; the potential of hydrogen of a stratum is balanced; and the remediation method is suitable for the large-area hexavalent chromium polluted stratums different in potential of hydrogen and moisture content.

Description

technical field [0001] The invention belongs to the technical field of civil engineering and environmental geotechnical engineering, and specifically relates to a restoration method of hexavalent chromium-contaminated soil and groundwater, which can be used in restoration projects of hexavalent chromium-contaminated strata in landscaping and construction , especially suitable for low-permeability hexavalent chromium polluted clay and silt soil. Background technique [0002] Unlike other toxic heavy metals, chromium exists in two valence states of hexavalent and trivalent in nature. Due to its oxidizing properties, hexavalent chromium can strongly corrode and destroy organisms. It is one of the three internationally recognized carcinogenic metals, while trivalent chromium is an essential trace nutrient element for humans and animals, but excessive intake will also cause Harmful to the human body. Chromium and its compounds have been widely used in various fields of modern i...

AI Technical Summary

Problems solved by technology

Due to its oxidizing properties, hexavalent chromium can strongly corrode and destroy organisms. It is one of the three internationally recognized carcinogenic metals, while trivalent chromium is an essential trace nutrient element for humans and animals, but excessive intake will also cause Harmful to the human body

[0003] The current treatment technologies for hexavalent chromium-contaminated soil include in-situ and ex-situ remediation, both of which have limitations to varying degrees and are not conducive to large-scale promotion and use.

Among them, due to the need to move the soil, the ex-situ repair has a lot of earthwork workload and a large degree of damage to the rock-soil environment, so it is only suitable for the restoration of a small amount of soil.

While the current in-situ remediation method is widely used, it also has the following problems: cement solidification / stabilization technology adds cement to the soil to make the contaminated soil form a stable solidified body, and then hexavalent chromium and trivalent chromium It is sealed and wrapped in an inert matrix, which reduces the ability of chromium in the soil to migrate to the surrounding environment, but it does not change the form of hexavalent chromium, and there is a hidden danger of re-pollution in the solidified polluted soil in a complex environment; at the same time, the high cement solidification Alkalinity will change the acid-base balance of soil and water, and have adverse effects on surrounding organisms; the soil strength after remediation is high, which is not conducive to subsequent sampling testing and earthwork excavation operations; in addition, cement solidification / stabilization technology will pollute hexavalent chromium Poor treatment of groundwater

Soil washing method is to repeatedly wash chromium-contaminated soil by injecting a chemical solution with high extraction or reduction ability through point wells, and then extract the chromium originally adsorbed in the soil into the solution and reduce it to trivalent chromium. The amount of chemical used is large, the acid-base environment is single, and the reduction of hexavalent chromium and the precipitation of trivalent chromium cannot be guaranteed at the same time; and it is easy to cause changes in the physical and chemical properties of soil minerals, and it is not suitable for clay, silt and other low permeability coefficients. formation; in addition, the ferrous sulfate (FeSO 4 ), sodium metabisulfite (Na 2 S 2 o 5 ), ferrous chloride (FeCl 2 ) and other reducing agents contain a large amount of corrosive anions, which will cause secondary pollution to the soil and groundwater, and the safety of cement, steel bars and other structures in dangerous underground projects

Bioremediation is to reduce the accumulation of chromium in soil and groundwater by planting special plants or adding microorganisms in contaminated soil. However, the depth of phytoremediation is limited, and it can only treat shallow chromium-contaminated soil and groundwater. , and the restoration period is long, and the chromium-enriched plants need to be reprocessed; while the microbial restoration technology has strict requirements on environmental conditions such as temperature and pH, which are difficult to meet during on-site construction, and its restoration efficiency is easily affected

Electroremediation is an emerging in-situ soil remediation technology in recent years. Its basic principle is to add a low-voltage DC electric field to both ends of the chromium-contaminated soil, and use the effects of electric field electroosmosis and electromigration to remove chromium from the contaminated soil. It is usually only suitable for small-scale polluted sites, and its repair ability is easily affected by the dissolution and desorption of pollutants, carbonates in the soil, iron minerals, etc., and it is not suitable for acidic environments and low water content formation

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