硫化物吸附金属离子的实验研究──Ⅱ．温度与介质条件的影响

EXPERIMENTAL STUDY ON ADSORPTION OF METAL IONS ONTO SULFIDES──Ⅱ. INFLUENCES OF TEMPERATURE AND MEDIUM CONDITIONS

合成ＰｂＳ和ＺｎＳ对Ａｇ２＋、Ｃｕ２＋、Ｃｄ２＋、Ｆｅ２＋、Ｍｎ２＋、Ｍｇ２＋、Ｓｂ２＋和Ｂｉ３＋等离子吸附量与温度关系的实验研究表明，其遵从Ｋｅｌｖｉｎ公式：在Ａ类吸附，即抗衡离子交换型吸附中，温度上升，其吸附量升降由反应热决定，本实验中Ａ类吸附多为上升型；而大部分Ｂ和Ｃ类吸附，即朗谬尔型及反朗谬尔型的吸附量则随温度上升呈指数下降。例外的仅有ＰｂＳ对Ｂｉ３＋离子的吸附，其吸附量随温度上升有微弱的上升。这可能与Ｂｉ３＋离子和吸附剂ＰｂＳ之间共晶反应和铅的铋硫盐的形成有关。Ａ类吸附的吸附量受介质条件变化影响很少。但对Ｂ和Ｃ类吸附，吸附量受ｐＨ和离子强度变化影响取决于三个因素：①吸附剂ＰｂＳ、ＺｎＳ表面电荷特性；②溶液介质条件变化时吸附离子在溶液中离子态的分布与变化；③被吸附离子在吸附剂中扩散和形成化合物或共晶的能力。因此，当ｐＨ增加时，Ｐｂｓ和ＺｎＳ对金属离子吸附量的变化表现出多样性：增加的有ＰｂＳ对Ｆｅ２＋离子的吸附；下降的有ＰｂＳ对Ｓｂ３＋离子的吸附和ＺｎＳ对Ｆｅ２＋、Ｍｎ２＋离子的吸附；不变的有ＰｂＳ对Ｂｉ３＋、Ｚｎ２＋离子的吸附和ＺｎＳ对Ｍｇ２＋离子的吸附。当溶液中离子强度增加时，由于溶液中自由态离子?

The influence of temperature and medium conditions(pH and ionic strength) on the adsorption densities of ions Ag+, Cu2+, Cd2+, Zn2+, Fe2+, Mn2+, Mg2+, Sb3+and Bi3+on sulphides ZnS and PbS were studied. For the A-type, i.e. counter-balance ionic exchange-type adsorption, no remarkable variation of adsorption densities was observed and near 100 percent adsorptions were usually obserded as the temperature, pH value, and ionic strength in solution range from 30℃ to 80℃ , 2 to 6, and 0 to 0.5 mol / L, respectively. This is particularly true when the adsorption equilibrium constant is greater than 106. However, a decrease of 0.5%-0.6% in adsorption density was observed for Cd2+adsorbed by ZnS for its reaction constant is about 105when the pH value and ionic strength increase. Meanwhile, the adsorption density of Cd2+on ZnS increases when the temperature raises for it speeds up the ionic exchange reaction. For B- and C-types of adsorptions, i.e. Langmuir and reversed Langmuir types, the adsorption densities decrease exponentially with the increase of temperature.However, the influence of medium conditions on adsorption densities depends on the following factors: (1) the surface charges on the absobents; (2) the species distributions and variations of adion in solution as the medium conditions changes; (3) the diffusion ability of the adions into the absorbent and ability of cocrystallization. With the increase of PH, the adsorption density may decrease (e.g. Sb3+on PbS, Fe2+and Mn2+on ZnS), increase(e.g.Fe2+on PbS), or remain unchanged (e.g. Bi3+and Zn2+on PbS and Mg2+on ZnS). The ionic stength exerts an influence on adsorption density through the species distributions in the solution.As a general rule, increasing ionic strength might result in a decrease of adsorption density.Actually, only the adsorption densities of ions Fe2+and Sb3+on PbS obey the rule.Meanwhile, the adsorption densities of Fe2+and Mn2+on ZnS increase, and those of Zn2+on PbS and Mg2+on ZnS remain unchanged.