Study On Physicochemical Properties And Element Release Of Sand-gravel Under Freeze-thaw-dry-wet Cycle

This paper focused on the problem that physicochemical properties and element release of sand-gravel are unknown under freeze-thaw-dry-wet cycles,the main gravel-sand(grey-green slate)in Huanxiangshan area was taken as the research object.Based on the mineral composition,element composition and physicochemical properties,the indoor freeze-thaw-dry-wet cycles experiment was carried out with simulating local natural environment.Under the freeze-thaw-dry-wet cycles,two factors(salinity,gravel-sand particle size)random design test were used to observe the quality,surface morphology,microstructure,porosity,mineral composition and content of gravel-sand treated with different particle sizes and salinity,and the EC,pH,element composition and content of gravel-sand leaching solution are explored.The effects of particle size,salinity and freeze-thaw-dry-wet cycles on physicochemical properties and element release of sand-gravel were studied,and the main influencing factors and related functions are determined.The main conclusions are as follows:(1)Loss and cumulative loss rate of mass of gravel-sand are negatively correlated with particle size,and are positively correlated with salinity,freeze-thaw-dry-wet cycles,the relationship between the cumulative loss rate of gravel-sand mass with different particle sizes and salinity and freeze-thaw-dry-wet cycles is a linear increasing function,and factors that affects the cumulative loss rate of gravel-sand mass is freeze-thaw-dry-wet cycles>particle size.The degree of surface morphological damage,microstructural damage and porosity of gravel-sand are negatively correlated with salinity and freeze-thaw-dry-wet cycles,and factors affecting the porosity of gravel-sand are freeze-thaw-dry-wet cycles>particle size.(2)The EC and pH of the gravel-sand leaching solution treated with different particle sizes and salinity increased first and then decreased as the particle size increased,and increased with the increase of the salinity and freeze-thaw-dry-wet cycles.Minerals whose mineral content is positively related to particle size are muscovite,albite and chlorite,negatively related to particle size are quartz and calcite,positively related to salinity are muscovite,chlorite and calcite,negatively related to salinity are quartz and albite,and positively related to freeze-thaw-dry-wet cycles are muscovite,chlorite and calcite,negatively related to freeze-thaw-dry-wet cycles are quartz and albite.The factors affecting the content of quartz,muscovite and albite are the particle size,and the remaining minerals have no significant factors.The structural characteristics of gravel-sand and the existence of fissures and hydrophilic minerals in it,freeze-thaw weathering,water-rock interaction,and salt participation in leaching are the main causes of freeze-thaw-dry-wet cycles destruction of gravel-sand.(3)At the same salinity level,element leaching types and leaching cumulative rate decreased with the increase of particle size and freeze-thaw-dry-wet cycles.Leaching mass and leaching rate decreased with the increase of particle size,and increased first and then decreased with the increase of freeze-thaw-dry-wet cycles.Leaching cumulative mass decreased with the increase of particle size,and increased with the increase of freeze-thaw-dry-wet cycles.(4)At the same particle size level,the element leaching types of 2mm and 10mm gravel-sand decreased first and then increased as the salinity increases,while the salinity of 20mm and 30mm have no significant difference with the increase of salinity.Element leaching types decreased with the increase of freeze-thaw-dry-wet cycles.When particle is 2mm,the law of leaching mass of gravel-sand with salinity is different from the rest of the particle size.When particle are from 10mm to 30mm,except for the 20th,the leaching mass reduced first and then increased with the increase of salinity.Leaching mass increased first and then decreased with the increase of freeze-thaw-dry-wet cycles.Except for 2mm,the leaching cumulative mass of the other size gravel-sand decreased first and then increased with the increase of salinity,and increased with freeze-thaw-dry-wet cycles.The leaching rate and leaching mass are consistent.The leaching cumulative rate was faster when the high-salinity treatment of 10mm?30mm gravel-sand.(5)Under different particle size and salinity treatments,element leaching types of gravel-sand are more than 21,and decreased with the increase of freeze-thaw-dry-wet cycles.Leaching mass and leaching rate increased first and then decreased with the increase of freeze-thaw-dry-wet cycles,and leaching cumulative mass show a logarithmic function relationship with the increase of freeze-thaw-dry-wet cycles.(R2>0.9227),leaching cumulative rate presents a quadratic polynomial function as freeze-thaw-dry-wet cycles increases(R2>0.651 8).Particle size is the dominant factor for the leaching cumulative rate and K/Na,salinity is the dominant factor for the leaching mass,leaching rate and Ca/Na,and the freeze-thaw-dry-wet cycles is the dominant factor for element leaching types and leaching cumulative mass.