Potassium pyrophosphate is an environmentally friendly substance for farmland soil. The elution characteristics of the prepared potassium pyrophosphate eluent on heavy metal copper in simulated contaminated soil were studied through a batch oscillating elution experiment. The elution effects of elution time, eluent pH and potassium pyrophosphate concentration on the elution were discussed. The influence of copper in soil under the action of potassium pyrophosphate eluent and the change characteristics of heavy metal speciation before and after elution were discussed. The results show that the longer the elution time and the greater the eluent concentration, the better the elution effect. The experimental conditions were optimized, leaching and leaching for 24 hours, the pH of the eluent was 7.0, n (potassium pyrophosphate):n (copper) was 7:1, the elution effect was good, and the copper elution rate was 40. 51%. The copper eluted by potassium pyrophosphate is mainly in the acid-extractable state and the reducible state. The leaching process of soil copper by potassium pyrophosphate eluent conforms to the double constant equation, indicating that the desorption of copper in soil under the action of potassium pyrophosphate eluent is a heterogeneous diffusion process.
Heavy metal pollution poses a huge threat to the environment on a global scale due to its easy accumulation and non-biodegradability. At present, the area of cultivated land contaminated by heavy metals in my country is about 20 million hm2, accounting for about 1/6 of the total cultivated land area. Although copper is an essential element for plant growth, excess copper in soil, especially high concentrations, is considered one of the most dangerous pollutants.
In recent years, research on how to effectively remove the heavy metal element copper from contaminated soil has received widespread attention. Complexing agent ex-situ leaching technology is considered an effective method to remediate heavy metal contaminated soil. The addition of complexing agent can increase the content of soluble heavy metals in the soil solution, which is beneficial to the leaching and removal of heavy metals in contaminated soil.
Commonly used eluants include inorganic eluants, organic eluants and surfactants. Different eluants have different effects on removing heavy metals from contaminated soil. Ethylenediaminetetraacetic acid (EDTA) is a commonly used eluent. Liu Xia et al. used EDTA to elute and repair Cu and Pb in artificially contaminated soil. Its removal efficiency of Cu and Pb was better than that of citric acid and rhamnolipid. . Due to EDTA’s poor biodegradability, long retention period in the environment, and high risk to groundwater, people are now paying more attention to the use of biodegradable and environmentally friendly eluents to remediate heavy metals in contaminated soil. YANG et al. used ethylenediamine disuccinic acid (EDDS) to elute heavy metals in soil contaminated by electronic waste. When the EDDS concentration was 1. 26 mol·kg-1 soil, the elution of Cu, Pb, Zn and Cd was The efficiency is equivalent; Deng Hongxia and others used saponins to perform a single leaching remediation of Cu and Pb in single-polluted and composite-polluted soils. The removal rates of Cu and Pb were 29. 02%, 25. 09% and 31. 56% respectively. ,28.03%. Although complexing agents and surfactants such as EDDS are biodegradable, they are usually expensive, limiting their large-scale engineering applications. Therefore, it is crucial to choose an environmentally friendly and inexpensive complexing agent.
Potassium pyrophosphate is mainly used in cyanide-free electroplating to replace sodium cyanide as an electroplating complexing agent. It is also used to prepare cleaning agents, detergents, and iron ion removal reagents in bleaching and dyeing; in the food industry , used as emulsifier, chelating agent, tissue improver, etc. The phosphorus, potassium and other elements contained in potassium pyrophosphate are nutrients for plant growth. It is an environmentally friendly substance for farmland soil. However, there are few reports on its use as a remediation agent for the leaching and remediation of heavy metals in contaminated soil. .
This article uses potassium pyrophosphate solution as the eluent to elute heavy metal copper in contaminated soil, and explores the effects of elution time, eluent pH, eluent concentration and other factors on the elution effect, and The changes in the forms of copper in the soil before and after the experiment were analyzed using the Community Bureau of Repvc Stabilizer Reference (BCR) step-by-step extraction method, and desorption kinetic analysis was used to study the mechanism of leaching to remove copper from the soil.
After repeated explorations, we came to the following three conclusions.
1) Elution time, eluent pH and concentration have an important impact on copper removal. As the leaching time is extended, the leaching rate increases; when pH < 4. 0, the leaching rate decreases rapidly as the pH value increases, and in the range of pH 5. 0 to 9. 0, the removal rate slowly increases; The washing effect increases as the concentration of potassium pyrophosphate increases, but the higher the concentration, the lower the unit desorption amount. Optimizing the experimental conditions, the pH of the eluent = 7.0, n (potassium pyrophosphate):n (copper) is 7:1, and the elution effect is good. After 24 hours of elution and extraction, the copper elution rate is 40.51 %.
2) The heavy metals eluted by potassium pyrophosphate are mainly acid-extractable and reducible states. After leaching experiments, the proportions of the two forms were reduced from 52. 21% and 34. 57% to 18. 83% and 23. 62% respectively, which reduced the bioavailability of heavy metal copper in contaminated soil.
3) The optimal model for potassium pyrophosphate to desorb copper from contaminated soil is a double constant equation, indicating that the desorption is a heterogeneous diffusion process.
