粟米糠-耐Pb菌株复合吸附剂固定床穿透曲线特性

以粟米糠(MC)为原料,添加自铅锌尾矿渣中分离的耐铅菌米曲霉(HA)制成粟米糠-耐Pb菌株复合吸附剂(MCH),研究固定床系统中MCH对Pb~(2+)的动态吸附特性,考察吸附柱高度、初始离子浓度、进水流速对穿透曲线特性的影响.研究结果表明,复合吸附剂在固定床系统中的吸附性能明显优于单一吸附剂;MCH对Pb~(2+)的吸附穿透时间与吸附柱高成正相关,与初始离子浓度和进水流速成负相关,传质区长度与吸附柱高成负相关,与初始离子浓度和进水流速成正相关;初始离子浓度对穿透曲线和传质区长度影响最小.采用BDST、Yoon-Nelson和Thomas模型拟合试验数据结果显示,在较高流速和初始离子浓度条件下,实测与BDST模型拟合数据的相对误差最小,其原因可解释为BDST模型忽略了内部扩散和质量传递间阻力的影响;在吸附柱较低、初始离子浓度或进水流速较大条件下,由于传质推动力过大以至传质区被瞬间穿透,吸附质在吸附柱内停留时间很短,Yoon-Nelson和Thomas模型无法准确预测其穿透时间和拟合穿透曲线;总体上对比其它模型,Thomas模型拟合穿透曲线的效果较好,说明在MCH固定床Pb~(2+)的吸附过程中没有轴向扩散且具有平推流作用.

The breakthrough curve of adsorbent bed for Pb2+ ion adsorption onto a fixed millet bran-Pb tolerant strain composite

A millet bran-Pb tolerant strain composite adsorbent (MCH) was prepared by mixing lead tolerant strains, Aspergillus oryzae, isolated from lead and zinc mine tailing wastes, with millet bran (MC). experiments were carried out to investigate the kinetics and characteristics of Pb²⁺ ion adsorption and the influences of adsorption column height, initial Pb²⁺ ion concentration and influent flow rate on the breakthrough and mass transfer zone height. The results show that MCH gave significantly higher Pb²⁺ removal rate than MC. The time for penetration of Pb²⁺ ion adsorption onto MCH was positively related to column height but negatively related to both initial ion concentration and influent flow rate. On the contrary, the length of mass transfer zone was negatively related to column height but positively related to both initial ion concentration and influent flow rate. The obtained experimental data were further analyzed by using BDST, Yoon-Nelson and Thomas models. At relatively high flow rate and initial ion concentration levels, BDST model fit the data well and gave the lowest relative deviation between the measured and estimated values. This could possibly be attributed to that in the BDST model, the influence of internal diffusion and mass transfer resistance was neglected. Within the range of low column height and high initial ion concentration and influent flow rate, the mass transfer zone was instantly penetrated due to excessively high mass transfer power, resulting in short residence time of the adsorbate in the adsorption column. Under such conditions, both Yoon-Nelson and Thomas models failed to fit the breakthrough curves and thus could not be used to predict the breakthrough time. In general, Thomas model better fits the breakthrough curve in the tested range than the other two models, suggesting that there is an oriented smooth flow with insignificant axial diffusion for adsorption process in the fixed bed.