Study On The Effect Of Phosphogypsum On The Stability Of Yellow Soil Aggregates

Phosphogypsum is an industrial waste produced by the production of wet-process phosphoric acid,and it can only be used for storage treatment,which not only takes up land resources,but also pollutes the environment.Therefore,the efficient use of phosphogypsum has always been the focus of attention.The application research of phosphogypsum in agriculture mainly includes the effects on soil water permeability,microbial enzyme activity,crop yield,and improved soil acidity and alkalinity,etc.However,there are few studies on the effect of phosphogypsum on the composition and stability of soil aggregates.The size distribution and stability of soil aggregates are important indicators for evaluating soil physical properties and soil quality,which can directly affect soil structure and crop stability.Therefore,the use of phosphogypsum to improve the stability of soil aggregates can not only solve the major problem of environmental pollution caused by its large accumulation,but also add a green path to realize the"self-production and self-consumption"of phosphogypsum for its application in agriculture.Based on this,this article takes the acid yellow soil of Guizhou as the research object,exploring the effects of undisturbed phosphogypsum(PG),washed phosphogypsum(WPG),phosphogypsum lotion and soluble substances in phosphogypsum on acidity,the size distribution and stability of aggregates,and three forms of inorganic cementitious iron oxide(free state Fed,amorphous state Feo,complex state Fes),finally,proposing the influence mechanism of the incorporation of phosphogypsum on the p H,aggregate stability and the content of three forms of iron oxide in yellow soil.First,mix PG and WPG into yellow soil separately,when the dosage is increased from 0g/kg to 96 g/kg,the p H of the yellow soil of the former increased from 4.80 to 4.95 and then decreased to 4.65;the p H of the yellow soil of the latter increased from 4.80 to 5.61 and then decreased to 5.30;among them,when PG and WPG are mixed at 6 g/kg and 24 g/kg,the p H of yellow soil increases the most.The p H of yellow soil was significantly reduced under the cultivation of phosphogypsum lotion.The reason is that the washed PG takes away most of the free phosphoric acid,resulting in weak acidity of WPG and strong acidity of the phosphogypsum lotion.Therefore,the effect of WPG in improving the acidity of yellow soil is better than that of PG,and the phosphogypsum lotion will increase the acidity of the yellow soil.It shows that the content of free phosphoric acid in phosphogypsum plays a leading role in the acidity of yellow soil.Different amounts of PG,WPG and different concentrations of phosphogypsum lotion were applied to the yellow soil.It was found that the number of aggregates>2 mm in the yellow soil under various culture conditions was significantly increased,and the number of agglomerates<0.25 mm decreases.The content of PG and WPG were 6 g/kg and 24 g/kg and the concentration of phosphogypsum lotion ratio is 3:10,respectively,the aggregate index average weight diameter MWD was the largest,the aggregate destruction rate PAD and the fractal dimension D was the lowest,and the yellow soil aggregates had the best stability.The effect of different dosages of PG and WPG on the content of iron oxides in yellow soil is Fed>Feo>Fes.Among them,When the dosages of PG and WPG are both 6 g/kg,the content of Fed and Fes is the highest;and when the content of both is 12 g/kg,the content of Feo is the highest.Since the more iron oxide content of each form,the more it can promote the formation of aggregates in yellow soil,so the application of PG and WPG can increase the content of iron oxide in yellow soil,thereby promoting the formation of aggregates and improving the stability of aggregates.Secondly,to simulate the soluble composition in phosphogypsum,different concentrations of CaSO₄,SO₄^2-,PO₄^3-and F^-solutions all increased the p H of yellow soil to some extent.This is becauseSO₄^2-and PO₄^3-ions are easily coordinated with the hydroxyl groups on the surface of the yellow soil to release OH^-,and at the same time,F^-will also complex and exchange with the Al-OH groups on the surface of the yellow soil particles to release OH^-,soSO₄^2-,PO₄^3-and F^-can also regulate the acidity of yellow soil.The effects of solutions of different concentrations on the stability indexes MWD and PAD of yellow soil aggregates are shown as follows:CaSO₄>F^->SO₄^2->PO₄^3-.Among them,the number of aggregates less than 0.25 mm under each culture was lower than that of CK samples,indicating that the single application of soluble substances in phosphogypsum can promote the formation of aggregates,increase the number of large aggregates,and improve the stability of yellow soil aggregates.The degree of influence of CaSO₄,SO₄^2-,PO₄^3-and F^-solutions culture on various forms of iron oxide is expressed as Fed>Feo>Fes.Except that Feo content was lower than CK sample after 28 days of NaF solution culture,the content of iron oxide in all forms at other concentrations was significantly higher than that of CK culture,indicating that the application of each component in phosphogypsum can increase the content of iron oxide in various forms in the yellow soil,and promote the agglomeration of micro-aggregates under the action of cementation,thereby forming more large agglomerates and improving the stability of the agglomerates.