Geochemical fractionation and potential release behaviour of heavy metals in lead‒zinc smelting soils

The lack of understanding of heavy metal speciation and solubility control mechanisms in smelting soils limits the effective pollution control. In this study smelting soils were investigated by an advanced mineralogical analysis (AMICS), leaching tests and thermodynamic modelling. The aims were to identify the partitioning and release behaviour of Pb, Zn, Cd and As. The integration of multiple techniques was necessary and displayed coherent results. In addition to the residual fraction, Pb and Zn were predominantly associated with reducible fractions, and As primarily existed as the crystalline iron oxide-bound fractions. AMICS quantitative analysis further confirmed that Fe oxyhydroxides were the common dominant phase for As, Cd, Pb and Zn. In addition, a metal arsenate (paulmooreite) was an important mineral host for Pb and As. The pH-stat leaching indicted that the release of Pb, Zn and Cd increased towards low pH values while release of As increased towards high pH values. The separate leaching schemes were associated with the geochemical behaviour under the control of minerals and were confirmed by thermodynamic modelling. PHREEQC calculations suggested that the formation of arsenate minerals (schultenite, mimetite and koritnigite) and the binding to Fe oxyhydroxides synchronously controlled the release of Pb, Zn, Cd and As. Our results emphasized the governing role of Fe oxyhydroxides and secondary insoluble minerals in natural attenuation of heavy metals, which provides a novelty strategy for the stabilization of multi-metals in smelting sites.     

Mobility of Different Phosphorus Pools in the Sediment of Lake Dianchi during Cyanobacterial Blooms

By the method of P fractionation, we examined sedimentary P fractions in Lake Dianchi before and during cyanobacterial blooms, namely in April 2004 and August 2004, respectively. In this study, the whole lake is divided into four areas to discuss P fractions in sediment and the relationship between them and water quality or the nutrient status. The results show that where the water body was much more eutrophic (higher levels of total phosphorus, total nitrogen, chlorophyll and trophic status index) in Lake Dianchi, there can be more potentially available phosphorus (BD–P and NaOH–P) and less no available phosphorus (HCl–P and residual P) in the corresponding sediments. Statistical analysis and statistical plots are used to compare the distribution of every P fraction during cyanobacterial blooms with that before cyanobacterial blooms, and the results indicate that the different P fractions had the different mobility. HCl–P and residual P were relatively stable, while NaOH–P, BD–P and NH4Cl–P were more mobile. BD–P can intensively be released from sediment to water and consequently promote cyanobacterial blooms, and at the same time the NaOH–P concentration increased in sediment, which can result from that BD–P released can be partly immobilized to NaOH–P. During cyanobacterial blooms BD–P can be as a source, but NaOH–P as a sink. Besides, total phosphorus in sediment had no significant differences between two samplings.     

An approach for arsenic in a contaminated soil: Speciation, fractionation, extraction and effluent decontamination

The fractionation and speciation of As in a contaminated soil were investigated, and a remediation strategy was tested. Regarding speciation, we found that As(V) prevails over As(III) whereas more than 40% of total arsenic is in organic form. The fractionation of As was investigated with two sequential extraction methods: a low mobility was found. Then we tested the possibility of using phosphoric acid to extract As from the soil and cleaning the washing effluents by sorption onto montmorillonite. The efficiency of the extraction and of the adsorption onto the clay were also investigated for Cr, Cu, Fe, Mn, Ni, Pb and Zn, whose total concentrations and fractionation in the soil are reported here. The extraction percentages for As and metals ranged from 30 to 65%; the residual proportions in the soil are presumably in very unreactive forms. Montmorillonite showed a good uptake capacity towards the investigated pollutants.     

一种从有机废水中获取甲酸的方法

探讨了从环己醇/环己酮生产装置产生的酸性有机废水中获取甲酸的方法.在实验基础上,确定了共沸-分馏组合法回收甲酸的工艺过程、适宜挟带剂及工艺条件.采用共沸-分馏组合法处理该有机废水,可获取质量分数为80%以上的甲酸水溶液,甲酸回收率可达70%以上.同时,经本法处理后,该有机废水的COD由1.0×105～1.6×105 mg/L降至5× 102 mg/L以下,COD去除率达98%以上.