Effect Of Phosphogypsum On Acidity And Aluminum Form Of Yellow Soil And Its Mechanism

Yellow soil is one of the typical acid soils in my country,and it is also the largest soil in Guizhou.The overacidity of the soil not only leads to the decline of soil fertility,reduced cation content and restricted crop growth,but also activates a large amount of aluminum in the soil,further aggravating soil acidification.Soil acidification is mainly caused by the weathering of soil minerals,but a large amount of fertilization will also aggravate soil acidification.Due to environmental conditions and unreasonable soil fertilization,the acidification situation of yellow soil in Guizhou is becoming more a nd more serious.It is urgent to solve the problem of yellow soil acidification.The essence of soil acidification is the activation of soil aluminum and the hydrolysis of aluminum ions,reducing the active aluminum content of yellow soil,which can inhibit the process of soil acidification,thereby reducing the acidity of yellow soil.The traditional method of improving acid soil is to apply lime,but the frequent application of lime soil will cause double acidification and soil compaction.Phosphogypsum is a by-product of the production process of wet-process phosphoric acid.The current method of phosphogypsum treatment is mainly storage,which not only takes up land,but also pollutes the environment.According to the analysis of the solubility and soluble phosphorus and fluorine changes of phosphogypsum in different pH acidic solutions and yellow soil solutions,the physical and chemical properties of phosphogypsum and the soluble substances contained in it may have the effect of inhibiting aluminum toxicity and improving the acidity of yellow soil.Soil can not only alleviate soil acidification,but also solve the environmental pollution problem of phosphogypsum to a certain extent.In this paper,from the perspective of the effect of phosphogypsum on the acidity and aluminum forms of yellow soil and the mechanism of action,based on the investigation of the basic physical and chemical properties of phosphogypsum and its effects on the acidity and various forms of aluminum in yellow soil,the phosphogypsum raw material and yellow soil are used as the test soil.Using the method of simulating solid-solid mixing,solid-liquid mixing and liquid-liquid mixing culture experiments,the influence of calcium sulfate and soluble impurities on various forms of aluminum in yellow soil,as well as the influence mechanism of phosphogypsum on the acidity and aluminum forms of yellow soil were studied.Through the analysis of the physicochemical properties of phosphogypsum,investigating the changes in the solubility of p hosphogypsum and the content of soluble phosphorus and fluorine under the environmental conditions of yellow soil can provide a theoretical basis for the influence of phosphogypsum on the physical and chemical properties of yellow soil.According to the solid-solid mixed culture experiment,when the content of PG and WPG is in the range of 0-12g/kg soil,with the increase of gypsum content,culture temperature and time,the pH of each mixed soil sample rises,soluble aluminum,Ex-Al And Hy-Al content decreased,Or-Al content increased.After the PG content reached 12g/kg soil,the acidity of the mixed soil sample increased and the active aluminum content increased.And when the culture temperature and time are between 15??25?and 0?30d,the effect of phosphogypsum is the most obvious.In addition,the effect of PG on improving yellow soil is higher than that of WPG at a certain amount of gypsum,indicating that the soluble impurities in phosphogypsum have an effect on the acidity and aluminum form of yellow soil.The simulated solid-liquid mixed culture experiment showed that:under certain culture temperature conditions,different concentrations of CaSO ₄,SO₄^2-,H₂PO₄^-and F^-solutions reacted with yellow soil for different time.In a short period of time?0?2d?,with the increase of F^-concentration and cultivation time,the pH of yellow soil increases rapidly,and the aluminum activity of yellow soil decreases.After the cultivation time reaches 2d,with the concentration of CaSO₄,SO₄^2-and H₂PO₄^-and cultivation time With the increase,the pH of the yellow soil will increase and the soluble aluminum content will decrease.Under different temperature conditions,high temperature helps each solution interact with the yellow soil and reduce the Ex-Al and Hy-Al content of the yellow soil.The Or-Al content of the yellow soil does not change significantly after the action of the other solutions except the fluorine solution,indicating that phosphogypsum is added Calcium sulfate mainly affects the content of Hy-Al,while SO₄^2-,H₂PO₄^-and F^-mainly affect the content of soluble aluminum and Ex-Al.After different initial concentrations and pH of CaSO ₄,SO₄^2-,H₂PO₄^-and F^-solutions interact with yellow soil,under low p H conditions,H⁺action dominates.With the increase of different solution concentrations and pH,yellow soil Ex-Al and Hy-Al The content of decreased,the content of mononuclear aluminum hydroxy in the yellow soil solution decreased,and the content of Al-SO₄,Al-PO₄ and Al-F complexes in the solution was increased accordingly.Therefore,after phosphogypsum is added,it contains a lot of calcium and soluble impurities.In a short time,firstly,F-interacts with yellow soil.When F^-is exhausted,Ca²⁺,SO₄^2-and H₂PO₄^-interact with Al³⁺in yellow soil.Common reaction,in which H₂PO₄^-is the leading role,SO₄^2-is the secondary role,and Ca²⁺is the coordinating ion.The simulated liquid-liquid mixed culture experiment showed that when CaSO ₄,SO₄^2-,H₂PO₄^-and F^-solutions of different concentrations were added,the content of Al³⁺in the solution decreased and the content of Al-F increased;the aluminum activity in the solution decreased and the aluminum form changed.Through the effect of coexisting ionic solution on Al³⁺,the study shows that the effect of H₂PO₄^-and SO₄^2-on Al³⁺is better than that of H₂PO₄^-.When SO₄^2-,H₂PO₄^-and F^-coexist,the reduction of Al³⁺activity is more significant.Therefore,the dissolved Ca²⁺of phosphogypsum has an inhibitory effect on the Al³⁺activity in yellow soil.Among them,SO₄^2-complexes with Al³⁺,H₂PO₄^-complexes and precipitates with Al³⁺,F^-complexes with Al³⁺,SO₄^2-,H₂PO₄^-and F^-can react with the hydroxyl groups on the surface of soil particles,resulting in a significant decrease in aluminum activity in yellow soil.