pH值、硫酸根和温度对钢管管垢中铬释放的影响

Effects of pH,sulfate and temperature on chromium release from steel pipe scales

以市政供水管网钢管管垢为研究对象,将垢层由外向内分为表层、硬壳层和疏松多孔层.利用SEM、BET、XRD、XPS和分形态提取等技术对预吸附Cr(Ⅵ)前后的各层管垢进行表征和分析,并探究了pH值、SO_(4)^(2-)浓度和温度对各层管垢中Cr释放的影响.结果显示,钢管各层管垢的主要成分均为α-FeOOH,吸附性能排序为表层>疏松多孔层>硬壳层,管垢中铁元素大多以三价和二价形式存在,具有一定还原性.Cr(Ⅵ)通过物理和化学吸附富集于管垢,主要以铁锰氧化物结合态存在,表层管垢富集量最大.酸性环境、SO_(4)^(2-)浓度和温度的升高均会促进Cr的释放.强酸性条件下表层Cr释放浓度为中性条件下的2.76倍;SO_(4)^(2-)浓度增加使各层管垢的Cr释放量增加0.1~0.4倍;温度升高20℃,表层管垢的Cr释放量增加26.74%.

The scales of steel pipes in water distribution systems were researched by dividing them into a surface layer,a shell-like layer,and a porous core layer inward.We characterized and analyzed the three layers before and after the adsorption of Cr(Ⅵ) using SEM,BET,XRD,XPS,and Tessier sequential extraction and investigated the impact of pH,SO_(4)^(2-) concentrations and temperatures on the Cr release from each layer.Results showed that α-FeOOH was the primary component in all layers,and the adsorption capacity in the surface layer,porous core layer,and shell-like layer decreased in order.Iron scales existed mainly in Fe(Ⅲ) and Fe(Ⅱ)with certain reducibility.Cr(Ⅵ) could physically and chemically adsorb on the corrosion scales,mainly in Fe-Mn oxides.The amount of Cr accumulated on the surface layer was the largest.Low pH,high SO_(4)^(2-)concentration,and high temperature promoted the Cr release.Specifically,the Cr release concentration from the surface layer was 2.76 times under strong acidic conditions than under neutral conditions,the one from all layers was increased by 0.1~0.4 times with the increase of SO_(4)^(2-) concentration,and the one from the surface layer was increased by 26.74% with temperature increased by 20 ℃.