酸性矿山废水中铜在含铬施氏矿物上的吸附及其对矿物溶解与相转变的影响

Adsorption of Cu(Ⅱ) on chromate-doped schwertmannite and effect on the mineral's dissolution and phase transformation under acid mine drainage conditions

施氏矿物对水体中的重金属具有较强的吸附和固载能力,但随着环境条件的改变,施氏矿物可能会溶解并发生相转变,引起重金属的释放.利用化学合成的含Cr施氏矿物,探究其在不同Cu(Ⅱ)浓度与pH条件下含Cr施氏矿物的溶解和相转变.研究结果表明,在pH^3时,含Cr施氏矿物对Cu(Ⅱ)的吸附量较少,Cu(Ⅱ)对矿物溶解的影响不明显;在该pH条件下,含Cr施氏矿物会发生相转变生成部分针铁矿,但是随着溶液中初始Cu(Ⅱ)浓度的升高,矿物的相转变得到抑制.当pH升高至pH^5时,含铬施氏矿物对Cu(Ⅱ)的吸附量显著增加,Cu(Ⅱ)主要以Cu(OH)+与Cu2_(OH)_2^(2+)的形态吸附在含Cr施氏矿物表面,而高浓度Cu(Ⅱ)存在时也会生成部分Cu(OH)_2固体直接沉淀在矿物表面,覆盖矿物的反应位点从而阻碍SO_4^(2-)和CrO_4^(2-)的释放,而且随着Cu(Ⅱ)浓度的升高,这种抑制作用显著增强.在不同pH条件下,Cu(Ⅱ)的存在能够有效促进含Cr施氏矿物的稳定性,促进矿物对重金属Cr的固载能力,这些结果对酸性矿山废水环境中施氏矿物的稳定性和重金属污染控制具有重要意义.

Schwertmannite is an important scavenger for heavy metals in water environment. However,schwertmannite may undergo phase transformation with the change of environment,such as pH,redox conditions,and oxyanions or cations,thus leading to the release of heavy metals originally precipitated. This study investigated the dissolution and phase transformation of synthetic schwertmannite prepared in the presence of chromate,and with various Cu（ Ⅱ） concentrations at different pH. The results show that chromate-doped schwertmannite adsorbed small amount of Cu（ Ⅱ） at pH ~ 3,and the presence of Cu（ Ⅱ） has no significant effect on the dissolution of chromate-doped schwertmannite. Chromate-doped schwertmannite partially transformed into goethite in the absence of Cu（ Ⅱ） or with a relatively lower Cu（ Ⅱ） concentration at pH ~ 3,and the mineral＇ s transformation was delayed with the increasing initial copper concentration. While at pH ~ 5,chromate-doped schwertmannite adsorbed more Cu（ Ⅱ） compared with those at pH ~ 3. Cu（ Ⅱ） adsorbed on the surface of chromate-doped schwertmannite mainly in the form of Cu（ OH）＋and Cu2（OH）22＋. Additionally,high concentrations of Cu（ Ⅱ） favored the precipitation of Cu（OH）2 solid on the surface of schwertmannite at pH ~ 5. The adsorbed copper precipitate covered the mineral＇s reactive sites and delayed the release of sulfate and chromate from chromate-doped schwertmannite,and this kind of effect increased with theincreasing initial Cu（ Ⅱ） concentration. The presence of copper stabilized the structure of chromate-doped schwertmannite and promoted the immobility of chromate,which has important environmental implications for the stability of schwertmannite and the remediation of heavy metals under acid mine drainage（ AMD） conditions.