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Excessive lead can lead to reduced reproductive function and reduced immunity of organisms, including humans, which can lead to a variety of abnormalities. Lead pollution in the environment comes from three wastes discharged from lead-containing mining enterprises, the most important of which is tailings.
The use of continuous extraction method can accurately determine the biological characteristics in the soil, the method has been widely used, mainly Tessier method based continuous extraction method, this method has a more comprehensive impact on the evaluation of soil lead pollution, and the use of this evaluation method is also more detailed, there are three treatment methods for lead pollution in the current soil, namely: biological treatment, physical treatment and chemical treatment. Each of these three methods has different advantages and disadvantages. In recent years, by using the principle of lead pollution and the interaction mechanism of Qianyuling, it is used to regulate the environment of contaminated soil and extract phosphorus-containing substances for the remediation of lead pollution in soil, which has become the focus of international research in this field.
In China, Wang Xin et al. will calcium, magnesium, phosphate fertilizer can use heavy metals to control soil pollution, and achieved certain results, but in the research process, because the method of artificial metal aggravation is used in the study to implement soil pollution, rather than the soil generated by natural environmental pollution, and the relevant theoretical research on the formation mechanism of phosphorus and lead has not been involved in the study. The purpose of this experiment is that we use the continuous extraction method, which is an analytical method that can be used to study the morphology and mechanism of lead contaminated soil using the continuous extraction method, which can be used to study three phosphate fertilizers, namely calcium phosphate, phosphate ore powder and calcium-magnesium phosphorus fertilizer.
Materials and methods
Laboratory simulation culture This experiment uses a lead-zinc mine around the area, according to the research we found that the mining time of this mine has been more than 50 years old, now abandoned, due to unscientific opening caused by a large amount of tailings sand accumulated on the mountainside, after a long period of wind consumption and sunshine, the released aluminum has polluted a large area of soil.
This experiment according to the conventional sampling method, take a soil depth of about 20 cm sample, after air drying, and then reuse need to use nylon sieve 100 soil as a carrier, in this experiment we use different phosphate fertilizers including superphosphate, calcium, magnesium phosphorus fertilizer and low solubility phosphate ore powder, three phosphate fertilizers are 80 mesh nylon sieve, lower than some heavy metals in phosphate fertilizer, we can use nitric acid microwave digestion for quantitative analysis, and the use of atomic absorption for accurate content determination, Other properties in soil and phosphate fertilizers can be tested using conventional methods.
In this experiment, two phosphorus dosage detection levels were set according to the ratio of total phosphorus and molar ratio, and the proportions were 7.0 and 14.0. A total of seven experimental treatments, each with two replicates, two kilograms of air-dried soil samples were packed into 50 ml polycarbonate centrifuge tubes according to CK. Mineral phosphorus powder. 7.0 mineral phosphorus powder. 14.0 mineral phosphorus powder. 14.0 superphosphate. 7.0 superphosphate. 7.0 calcium, magnesium, phosphorus fertilizer. 14.0 calcium, magnesium, phosphorus fertilizer. The treatment method adds fertilizer, and it is necessary to mix it evenly, plus an appropriate amount of ionized water, so that the soil maintains a certain water content, at least to maintain the water holding capacity in the field, and then carry out the culture reaction at (25 Shi1) degrees for one month.
Assay method. After one month of cultivation, the lead element in the soil according to the Tessier continuous and graded extraction method to obtain various forms of lead element, namely, exchange state, water soluble state, organic bound state, residue state and other forms, we can treat the different forms formed by the lead element, all by taking the upper step residue, the soil-water ratio is strictly implemented in accordance with the regulations, and finally the supernatant is taken for testing.
(1) Lead distribution in contaminated soil. According to the results of the study, there is serious lead toxic pollution in the soil around the mining area.
Lead morphological composition and size ratio in soil In order, we need to intersect the least bioavailable residue state, which can be placed first, while the exchange state and water-soluble state with the highest biotoxicity are mainly due to the small proportion contained in the soil. However, the content is as high as 330 mg per kilogram.
According to the experiment, we found that the morphology of lead in the soil after phosphate fertilizer treatment changed, and the three phosphate fertilizers had a significant trend of reducing the content of different types of non-residue forms and lead in the soil, at the same time, the proportion of residual lead in the treated soil had an upward trend, and different types of phosphate fertilizer treated soil greatly reduced the amount of non-residue lead contained in the soil after lead pollution, and it was found that the application of the same phosphorus content of phosphate fertilizer to different varieties of phosphorus fertilizer in the soil at the stage of phosphate fertilizer, there is a certain difference in the degree of reduction of lead in non-residue form.
In this experiment, the form of lead in the soil contaminated by lead around the lead-zinc mining area of a city is mainly in the residual state, which may be caused by the accumulation of mountain lead over the years, and the tailings sand stacked on the mountainside can release and fix the lead element into the soil after weathering and chemical action, including secondary silicates and stable minerals, so the soil of the lead-zinc mining area of this experiment is mainly in the residual state, but the exchange state and water-soluble state content are high, and it has obvious biological toxicity. When the added phosphate fertilizer was treated, the composition of the lead morphology in the soil changed.
The three phosphate fertilizers used in this experiment, namely phosphate ore powder, calcium-magnesium phosphorus fertilizer, and superphosphate, can convert lead in various forms of lead content in soil and lead in organic binding states into more stable forms. This experiment shows that when phosphorus fertilizer with the same phosphorus content is added to the soil, calcium phosphate and calcium-magnesium phosphorus fertilizer will reduce the content of lead in the soil for the non-residue form of lead element, and this decline trend is very obvious.
In addition, the use of calcium phosphate phosphate fertilizer can significantly reduce the pH of the soil after the soil is dissolved, promote the carbonate organic matter in the soil to combine with the lead element, and quickly dissolve and release it, so that it reacts with the lead in the soil. At the same time, because phosphate ore powder is a poorly soluble neutral and insoluble phosphate fertilizer, it cannot provide water-soluble phosphorus, so it can form precipitated substances from lead elements in the soil.
However, phosphate ore powder has a considerable specific surface, which can adsorb a large amount of lead elements in the water-soluble and exchange states contained on the fixed soil solution and colloid, thereby significantly reducing the bioavailability effect of lead. Phosphate fertilizers can be used to reduce lead toxicity in soil.
Compared with other phosphate fertilizers, phosphate ore powder has better economy for remediating lead-contaminated soil, and this fertilizer is a long-lasting phosphate fertilizer, which can be extended over time compared with other two phosphate fertilizers, increasing the release and dissolution of phosphate ore powder phosphorus, and further fixing the non-residue lead element.
In this study, we analyzed the biological toxicity of soil lead for different zero fertilizers, including calcium-magnesium phosphate fertilizer, phosphate ore powder and calcium phosphate, and experimentally found that these three phosphate fertilizers can reduce lead toxicity, use the same content of phosphate fertilizer in the soil, except for phosphate ore powder, calcium phosphate and calcium-magnesium phosphorus fertilizer have basically the same effect on the removal of lead in soil fertilizer residues, and phosphate ore powder has a lower effect on the removal of lead in the non-residue state of soil.
However, the lead content in the non-residue state can be significantly reduced. When the molar ratio of phosphate fertilizer is 7 phosphorus fertilizer, it can fully meet the biological highest toxicity of reducing lead in soil. At the same time, the use of phosphate ore powder is the most economical and practical.