Preparation Of Humic Acid-based Phosphogypsum Soil Conditioner And Its Phosphorus Slow-Release Effect

Soil sanding is one of the most serious environmental problems in China.Soil sanding not only destroys the native vegetation,reduces biodiversity and intensifies soil erosion,but also causes ecological dysfunction and ecological degradation,which seriously threatens the survival and development of human beings.With the development of sandy soil improvement and management research,soil conditioner has become a hot spot in the current sandy soil improvement and management research.In this paper,we used weathered coal humic acid and phosphogypsum as the main raw materials and guar gum as the pelletizing additive to prepare humic acid-based phosphogypsum soil conditioner(HA-PG soil conditioner),and carried out research on the slow release effect and leaching effect of phosphorus in sandy soil and the improvement of physical and chemical properties of sandy soil.The main research contents and results are as follows:(1)The adsorption behaviour of water-soluble phosphorus in phosphogypsum and potassium dihydrogen phosphate was investigated using humic acid as adsorbent,and the adsorption process was more in line with the quasi-secondary kinetic model and Langmuir isotherm equation.The pH was around 5.Too high or too low a pH can lead to a decrease in adsorption capacity,and phosphogypsum can reduce the effect of pH on the adsorption effect.When phosphogypsum was used as the phosphorus source,the sandy soil sorbed more water-soluble phosphorus without desorption.Humic acid promoted the sorption of water-soluble phosphorus from the sandy soil and converted more of it into FeP-based slow-acting phosphorus.Phosphogypsum was more resistant to leaching than potassium dihydrogen phosphate,and the amount of water-soluble phosphorus leached from the sandy soil was reduced by 30.62%under the effect of leaching.(2)By designing single-factor tests and orthogonal experiments on the selection and dosage of pelletizing additive,the mass ratio of phosphogypsum to humic acid and the particle size distribution of soil conditioner,the main factors influencing the slow release effect of HA-PG soil conditioner in terms of watersoluble phosphorus,pH and electrical conductivity were investigated,The particle size distribution of the soil conditioner determines the slow release of watersoluble phosphorus,pH and conductivity,and the slow release effect is positively related to the particle size distribution of the soil conditioner.The formulation of HA-PG soil conditioner is based on a 0.3:1 mass ratio of phosphogypsum to humic acid,a guar gum dosage of 12.5%of the conditioner and a particle size of 6～8 mm to achieve the best slow release effect.(3)When granular and powdered soil conditioner were applied to the sandy soil,the effective phosphorus content increased by 25.14～39.75 mg·kg-1,the activation factor of phosphorus increased by 5.2%～8.68%,the electrical conductivity increased by 1.02～1.9 ms·cm-1,the organic matter content increased by 1.6～7.68 g·kg-1,the saturated water holding capacity increased by 1.77%～3.10%,and the pH by 0.18～0.59 at 60 day.The granular HA-PG soil conditioner had a slow-release effect of phosphorus,which helped to reduce the fixation of the sandy soil and reduce the leaching loss by leaching,water-soluble phosphorus leaching reduced by 21.88%.The effective phosphorus content,phosphorus activation factor,organic matter content and saturated water holding capacity of the sandy soil were positively correlated with the quality of humic acid,and humic acid was able to increase soil conductivity when the conductivity of the sandy soil was too low;pH and water-soluble phosphorus leaching were negatively correlated with the quality of humic acid.