The Study Of Characteristics On Ca²⁺ Adsorption-desorption By Different Land Use Patterns Of The Mingshan River Watershed Soil Inorganic Nanoparticles

This study investigates Ca2+sorption and desorption capabilities of inorganic nanoparticles in yellow earth and purple soil in Mingshan County. The soil samples are from five soil uses:forest, paddy field, tea plantation, dry land and orchard. Inorganic nanoparticles are first separated from soil by centrifuge to study their distribution patterns in each soil use, then analyzed by Langmuir and Freundlich adsorption isotherm equations about the sorption and desorption behavior towards calcium. Through studying the thermodynamics in the process above and by investigating soil components’influence on sorption and desorption, the Ca2+sorption mechanism of inorganic nanoparticles is captured. The comparison between sorption rates of Ca2+and K+provide reference for further study on inorganic nanoparticles’ sorption and desorption capabilities on metal ions. The findings of this study are as follows:(1) In yellow earth, inorganic nanoparticle amount in different soil use in descending order is:dry land, orchard, tea plantation, forest and paddy field; in purple soil:orchard, tea plantation, forest, dry land and paddy field. Both soils have seen the same amount features of organic matter, free iron oxide and CEC. Tea plantation has the most amounts of them and orchard the least.(2) Before and after the yellow earth sample was deprived of organic matter and free iron oxide, sorption amount of Ca2+shows a positive correlation with Ca2+concentration. Sorption amounts in descending order are:paddy field, tea plantation, dry land, forest and orchard. Purple soil dealt with the same method indicates the same correlation. Sorption amounts in descending order are:tea plantation, paddy field, forest, dry land and orchard. An improved fit to the Freundlich equations was found in terms of five soil uses in both yellow earth and purple soil. K value is in conformity with distribution pattern of organic matters, free iron oxide, CEC and the highest sorption amount in the greatest initial mass concentration.(3) Before and after the yellow earth sample was deprived of organic matter and free iron oxide, desorption amount of Ca2+increases over time. The increment trend is similar to that of the sorption. Desorption amount in descending order is again similar to that of the sorption amount:paddy field, tea plantation, dry land, forest and orchard. The conclusions above also apply to the case of purple soil. Before and after the yellow earth sample was deprived of organic matter and free iron oxide, desorption rate in descending order is orchard, forest, dry land, tea plantation and paddy field, the exact opposite order to desorption amount. Ca desorption rate in he purple soil dealt with the same method has a descending order of orchard, dry land, forest, paddy field and tea plantation, the exact opposite order to that of the desorption amount.(4) Before and after yellow earth and purple soil was deprived of organic matter and free iron oxide, different soil uses shows a sorption and desorption of K+pattern similar to that of Ca2+. However, at the same K+and Ca2+concentration level, inorganic nanoparticles in the same soil use varies greatly in desorption rates of these two ions.