Study On Enhanced Weathering And Soil-Forming Process Of Silicate Tailing Ore

The southwest region is rich in mineral resources and has a large number of tailings ponds.After the tailings ponds reach their service life,they need to be sealed.Conventional tailings pond closure and mine restoration mostly use toppe-vegetation restoration,but for the eco-fragile south-west mountainous region,where there is a shortage of rock and soil,to pay hundreds of thousands of square meters of tailings pond closure to pay soil,the traditional " Rob Peter to pay Paul " style to pay soil not only costs too much to fetch and transport,but also to destroy the secondary ecology of the extract area,so pay me to find a new source of soil for ecological restoration.The tailing sand is similar to sandy soil in mineral composition and particle size distribution,but the tailing sand has coarse particles and low cohesion in structure.In composition,it has the characteristics of low nutrient content and poor water and fertilizer retention ability.How to optimize and regulate the composition and structure of tailings sand,transform its property from bulk industrial solid waste to resource property,and use it as soil for ecological restoration of tailings pond closure will bring significant social,environmental and economic benefits to regional and industrial development.In view of the problems of slow weathering rate and unclear weathering control way of tailing ore,this study takes silicate tailing ore as the research object,combined with the characteristic of sulfide ore oxidation and acid production associated with tailing ore,studies the mineral decomposition and reconstruction process of silicate minerals in acidic environment,and establishes the weathering difficulty degree sequence of silicate minerals.The ion leaching and mineral decomposition processes of feldspar tin tailings and mica copper tailings under acidic conditions were analyzed,and the chemical weathering mechanism of two typical silicate tailings was clarified by combining with the morphological analysis of primary minerals and secondary minerals.Based on the climatic and environmental characteristics of tailing sand,the influence of freeze-thaw,cold-heat,dry-wet and other environmental elements alternating cycles on the weathering process was analyzed,and the soil properties such as grain size,porosity,density and bulk density of weathering products were analyzed.Ryegrass was planted in tailing sand weathering products,and the plant height,germination rate,dry weight and fresh weight of ryegrass were measured.The soil and ecological properties of tailing sand weathering products were evaluated in order to provide technical guidance for the rapid weathering of silicate tailing sand into soil.Specific conclusions are as follows:(1)The structure and composition of silicate minerals have a significant effect on the weathering process,and the degree of weathering difficulty is in the order of weathering intermediates(kaolinite,chlorite,montmorillonite)> feldspar(latase,potassium feldspar)> mica(biotite,Muscovite,auremica).Silicate minerals in acidic conditions due to the exchange of hydrogen ions and metal ions and mineral reconstruction,feldspar minerals metal ions in the order of calcium,potassium,magnesium,from the outside to the inside of the ion exchange.In mica minerals,the metal ions exchange from the surface and the cracks between layers in the order of calcium,magnesium and potassium.The leach layer on the surface of the main minerals produces small flake particles,and silicate and sulfate of aluminum,calcium and other elements appear in the weathering products.(2)A small amount of associated minerals in tailing sand play an important role in weathering process.Phosphate was detected on weathering products of tintail ore.Sulfates have been detected on weathering products from copper-tail ore.The leaching order of metal ions from feldspar-containing tin tailings is potassium >calcium > magnesium,and secondary minerals such as elostone and bauxite are formed on the surface of minerals during weathering.The leaching order of metal ions is calcium > potassium > magnesium,and the main secondary minerals are illite and vermiculite.On the whole,the chemical weathering of tailing sand can be regarded as the common weathering process of silicate minerals and metallic minerals.In addition to the weathering products of silicate minerals,the weathering process also contains the associated products such as metal sulfate.(3)The alternations of freezing and thawing,hot and cold,wet and dry can significantly improve the weathering process of tailing sand.The physical and chemical properties of tailing sand can be significantly changed through frequent changes of environmental conditions in a short period of time,such as the alternations of wet and dry,hot and cold,freeze-thaw,etc.The decomposition and reconstruction of minerals under acidic conditions increase the density of tailing sand and reduce the porosity.Physical weathering,such as alternating hot and cold,causes fissure expansion and porosity increase of tailing sand.When the tail ore was planted with ryegrass after rapid weathering,the germination rate increased by10% ～ 20%,the plant dry weight increased by 15% ～ 35%,the plant height increased by 4% ～ 10%,and the plant fresh weight increased by 5% ～ 30%.It is proved that the weathered tailings ore has the ability of ecological cultivation.