In the present work,release of hydrogen ions during
adsorption of copper ions by
variable charge soils was studied The results
showed that there was an abrupt charge in pH on neutralization curve of H,Al saturated variable charge soils,but no such an abrupt charge in pH could be observed when copper ions were added into the suspension of variable charge soils The two neutralization curves of variable charge soils with and without the addition of copper ions coincided each other when the pH of soil suspension was lower than a certain value,and separated obviously when the pH was higher than that value It is suggested that no
hydrogen ions were released after the addition of copper ions when the pH of soil suspension was lower than a certain value.This pH value was related to the content of iron oxide The larger the iron oxide content,the higher the pH value.For the majority of variable charge soils,this pH value was about 4 Kinetic studies on the release of hydrogen ions during
adsorption of copper ions by variable charge soils showed that the release of hydrogen ions consisted of a rapid process and a slow process For variable charge soils,the rapid process was getting less and less distinct when the pH approached about 4 from higher value At about pH4,the amount of hydrogen ions released after 10 min of addition of copper ions accounted for only 30% of that after 65 min of addition of copper ions The release of hydrogen ions by adsorption of constant charge soils was much quicker than that by adsorption of variable charge soils Even at pH 3 8,the amount of hydrogen ions released after 0 5min of addition of copper ions accounted for 56% of that after 65 min of addition of copper ions The exchange ratio H/Cu during the adsorption of copper ions was larger for variable charge soils than that for constant charge soils When 0 1 mol L -1 NaNO 3 was used as indifferent electrolyte in suspension of constant charge soils,the ratio H/Cu increased