The Study Of Adsorption Characteristics Of Polyacrylamide On Different Soil Layers Of Granite Collapsing Hill

In southern China granite hilly regions, collapsing hill is a special type of soil erosion, runoff erosion and soil has been saturated are major factors in the development of collapse of granite collapsing hill, exploring new and effective measures of collapsing erosion prevention is one of the hotspot of current research of water and soil conservation. PAM as a soil conditioner effect in soil erosion control and improving soil structure significantly. PAM improved soil structure mainly by promote soil small particles agglomerate into large aggregates. Currently, most of the research on PAM applied to collapsing erosion prevention focused on its applicability and increase infiltration and reduce erosion, etc., but the correlative report that research of the adsorption behavior of PAM in granite collapsing hill soil is less; the impact of PAM retained in the surface layer of soil on the ecological environment is also unclear. To better understand the effects and mechanism of PAM for the prevention and treatment of collapsing hill, in this paper, used three layers of typical granite collapsing hill soil:the red soil layer, the sandy soil layer and the detritus layer as the test subjects, study the PAM adsorption and retention characteristics at different soil layer of granite collapsing hill by laboratory simulation experiment. Combination of different adsorption conditions and adsorption thermodynamics quantitative discussed the adsorption mechanism and retention of PAM on different soil layers, determined applicable adsorption model, to provide the theoretical basis and technical indicators of the application of PAM in collapsing erosion control, the results showed that:(1) With the increase of the proportion of PAM liquid to soil, the adsorption of PAM on different soil layers of the collapsing hill rapidly increased first and then tended towards stabilized. The optimum liquid-solid ratio of PAM for the red soil layer and the sandy layer were 20:1; that was 25:1 for the detritus layer. When the concentration of PAM solution is 100-200 mg/L, the adsorption equilibrium time of sandy layer and detritus layer soil was 28-32 h; When the concentration of PAM solution is 300～500 mg/L, the adsorption equilibrium time was 20～24 h.(2) When the concentration is 100 mg/L, PAM solution can infiltrate and migrate normally in the soil column; When the concentration increased to 300～500 mg/L, the infiltration and migration were slow and difficult. As the concentration increased, the amount of PAM and deionized water for cleanout were reduced when reached the saturated retention states in the same soil layer. The detritus layer soil saturated retention status required the amount of PAM was less than red soil layer and sandy soil layer.(3) When the concentration gradually increased from 100 mg/L to 300 mg/L, the adsorption of PAM of sand layer and the detritus layer soil increased rapidly; when the concentration is greater than 300 mg/L, the adsorption variation amplitude decreased. The adsorption isotherm of the two soil layers accorded with Langmuir equation, the correlation coefficients was above 0.9.(4) With the increase of concentration, the retention of PAM was increased. The same concentrations of PAM solution had different effects on the amount of retention of different soil layer:the retention of red soil layer was presented the largest amount, the detritus layer soil was minimum, followed the sand soil layer.(5) The static adsorption capacity of PAM of red soil layer was almost zero, far less than the retention capacity; the retention capacity of PAM of sandy soil layer was greater than the static adsorption capacity, while the retention capacity of the detritus layer soil was less than the adsorption capacity, the main reason of these features were: under conditions of a concentrated solution, the solvent had impact on the adsorption capacity of PAM; there are differences of physical and chemical properties of different soil layer; except the intermolecular forces as well as mechanical trapping and hydrodynamic trapping when PAM was infiltrated and migrated in soil.