| Influence of simulated acid rain on soil acidification and nutrient ions (K+ and Ca +) leaching in different soil layers and adsorption/desorption kinetics of cations (K+, Ca2+ and Cd2+) in soils were studied by using the soil column method and flow-stirred techniques. The main results were obtained and some important conclusions were drawn as follows:1 A kinetic reaction device called as flow-stirred reactor was reasonably designed to investigate reaction kinetics of ions with soils, which has more advantages than traditional batch and flow methods. The solution in reaction chamber could be sufficiently mixed with soils at once and the rapid ion-exchange reactions could be observed. The unstable flowing rate caused by the block of clay particles had been solved and the effluent could be quantitatively and automatically collected according to expectation.2 The results of K+ adsorption kinetics in soils could be described by the first order kinetic equation and Elovich equation very well. For the different stimulated acid rain of pH2.5, pH3.5, pH4.5 and pH5.6, apparent adsorption amounts of K+ were 0.47, 1.68, 1.97, 2.24 mmol/kg, respectively, and apparent adsorption rate constant 0.08, 0.047, 0.043, 0.041 min-1, respectively. Langmuir equation could fit K+ adsorption in soils very well. Due to ion exchange reaction, H+ was released from soil surface into solution in the process of K+ adsorption. The specific adsorption of SO42-, main component of stimulated acid rain, made OH" release from soil surface and consume H+ in acidic soil system.3 The influence of pH 2.5 and pH4.5 simulated acid rain on soil acidity and K+ leaching in different soil layers indicated that pH of the beginning leachate collected from A, AB, and ABC soil layers was significantly different, which was pH4.0-4.5 in A layer and pH6.0~6.5 in AB and ABC layers, respectively. After 150-600 mm leaching volume, pH in the leachate of A, AB and ABC layers decreased to 3.8 at first and then increase slowly to maximal value dependent on soil layers (pH4.0~5.5). There was a peak value of electric conductivity (EC) in all leachates at the beginning stage, which showed that nutrient ions such as K+ and Ca2+ rapidly moved downwards. The loss of cations in soils was related to pH of acid rain and soil acidity. Potassium fertilizer applied in A-layer was almost leached out when using pH2.5 simulated acid rain. K+ leaching in A-layer was divided into the fast rate and the middle rate processes. As to pH 4.5 acid rain, there also existed fast and slow rate processes.4 Simulated acid rain had a direct impact on the acidity in surface soil andtransporting kinetics of exchangeable cations. After leaching with pH2.5 simulated acid rain, the content of exchangeable acid increased, and soil pH droped down from 4.57 to 3.5-4.2. Increase of exchangeable A13+ also showed decrease of acid buffer capacity and efficiency. However, pH value in AB layer increased 0.3-0.5 by leaching with pH4.5 acid rain. The different pH values of acid rain affected the transport and leaching of base cations in soils. Leaching amounts of exchangeable K+ with pH2.5 and pH4.5 acid rain accounted for 80-90% and 62-87% of that in original soil respectively; Leaching amounts of exchangeable Ca2+, 50-70% and 20-40%, respectively. The decrease of exchangeable Ca2+ and K+ elucidated the depletion of 'nutrient pool ', which caused the deterioration of soil fertility.5 The kinetic reaction characteristics of Ca2+ on red soil surface were investigated by using flow-stirred device. It showed that the processes of Ca2+ adsorption in soils were divided into rapid and slow reaction. Ca2+ adsorption fitted by first-order kinetics indicated that the maximal amounts remarkably decreased with increase of solution acidity, and Ca2+adsorption increased so rapidly with the rising of temperature as to get to adsorption equilibrium in advance. Ca2+ adsorption was also adequately described by parabolic diffusion and Elovich equations (R2>0.97). Diffusion rate constant remarkably de...
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