土法炼锌区废渣重金属固定研究

Immobilization of heavy metals of waste residue in indigenous zinc smelting areas

黔西北土法炼锌形成大量的废弃地,废渣重金属Zn、Pb和Cd全量分别为:7521、5365和53.4mg·kg-1,废渣的pH值为8.53,当地的背景土壤的pH值为5.39。重金属污染是当地面临的主要问题,同时也是土地复垦需要考虑的首要问题,目前来说防止重金属的迁移扩散显得尤其必要。用优级纯硝酸调控废渣的pH值检验pH值降低时废渣重金属释放程度;用碱石灰、活性炭、粉煤灰和有机质对重金属进行吸附;野外用碱石灰、纯碱和烧碱在土法炼锌区对废渣释放的重金属进行吸附。结果发现废渣重金属Pb、Zn和Cd随pH值降低而释放,Cd和Zn的释放量较大,pH值是影响重金属迁移扩散的重要因子;碱石灰、活性炭、粉煤灰和有机质对重金属吸附能力的比较得出碱石灰的吸附效果最好;野外实验进一步发现碱石灰固定重金属稳定性好、吸附性强。黔西北土法炼锌区有大面积的喀斯特地区分布,碱石灰来源广,用作废渣重金属释放的固定材料相对经济实用。

Due to indigenous zinc smelting, lots of lands were polluted and abandoned in north-western Guizhou Province, China. In these area, the total metal contents of Zn, Pb and Cd in the waste residue are 7 521, 5 365 and 53.4 mg-kgl, respectively. The pH value of waste residue is 8.53 while that of background soil is 5.39. Therefore, heavy metals pollution in the indigenous zinc smelting area becomes a serious environmental problem and relevant measures need to be adopted to control the migration of heavy metals. In this study, the adsorption capacities of four different adsorbents which were alkali lime, activated carbon, fly ash and organic matter were determined in the laboratory; the pH value of waste residue was adjusted with nitric acid to test the release of heavy metals when pH value was decreased; and then field experiments were also done to screen out a good adsorbent which can effectively re- duce the migration of heavy metals. The results indicated that： （I） the pH value is one of important factors that influenced the migra- tion of heavy metals. The soluble heavy metals （Pb, Zn, Cd） increased with the decreasing of pH value in waste residue and larger amount of Cd and Zn were released compared to Pb. （2） Alkali lime was the best adsorbent which could effectively reduce the solu- ble heavy metals among four adsorbents （alkali lime, activated carbon, fly ash and organic matter）. （3） Field experiments also re- vealed that alkali lime was of good stability and strong adsorption to heavy metals. In conclusion, alkali lime can effectively control the migration of heavy metals and a large area of karst in indigenous zinc smelting area of north-western Guizhou Province makes this both economical and practical.