可变电荷土壤吸附铜离子时氢离子的释放

RELEASE OF HYDROGEN IONS DURING ADSORPTION OF COPPER IONS BY VARIABLE CHARGE SOILS

可变电荷土壤吸附铜离子后 ,土壤的中和曲线上不出现pH突跃 ,而变成一条平缓变化的曲线。当土壤悬液的pH低于一定数值时 ,加入铜离子后不释放氢离子。该pH值与土壤中氧化铁的含量有关。氧化铁的含量越高 ,该pH值越高。对于大多数可变电荷土壤 ,此pH值为 4左右。对可变电荷土壤 ,pH值越接近 4,氢离子释放的快速过程越不明显。在pH 4左右 ,加入铜离子后 1 0分钟时 ,释放的氢离子量仅占 6 5分钟时释放量的 3 0 %左右。但当pH值高于 4 5时 ,在大多数情况下 ,加入铜离子后半分钟时释放的氢离子量即可占 6 5分钟时的 5 0 %以上。恒电荷土壤吸附铜离子时氢离子的释放速度比可变电荷土壤快得多。即使pH值低至 3 8,在加入铜离子后半分钟时氢离子的释放量即占 6 5分钟时的 5 6 %以上。可变电荷土壤吸附铜离子时的H/Cu比比恒电荷土壤大得多。当恒电荷土壤悬液中加入0 1mo1L- 1 NaNO3作支持电解质时 ,吸附铜离子时的H/Cu比增大。

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