Bench-scale soil column experiments were carried out to evaluate the effectiveness of Cr（VI） bioremediation process in soils by using indigenous bacteria with the addition of bacteria nutrient media. Effects of particle size, spray intensity, initial Cr（VI） concentration, circulation mode and soil depth on Cr（VI） remediation were studied. Results show that soils after 6 d remediation with spray intensity controlled in the range of 29.6-59.2 mL/min could well fulfill the requirement of concrete aggregate and roadbed material usage, for the leaching toxicity concentration of the Cr（VI） in treated soils under the chosen condition is far less than 5 mg/L The leaching toxicity and fractions of both hexavalent chromium and trivalent chromium from remediated soils were determined and compared with that of untreated soil. The results show that water soluble Cr（VI） declines from 1520.54 mg/kg to 0.68 mg/kg, exchangeable Cr（VI） decreases from 34.83 mg/kg to 0.01 mg/kg and carbonates-bonded Cr（V1） falls from 13.55 mg/kg to 0.68 mg/kg. Meanwhile, a corresponding increase in carbonate-bonded Cr（III）, Fe and Mn oxides-bonded Cr（III） and organic matter-bonded Cr（III） are found. It reveals that indigenous bacteria can leach out water soluble Cr（VI）, exchangeable Cr（VI） and carbonates-bonded Cr（VI） from contaminated soil followed by converting into carbonate-bonded Cr（III）, Fe and Mn oxides-bonded Cr（IlI）, organic matter-bonded Cr（III） and residual Cr（III）.
In order to provide the theoretical guidance for applying the neutralization method to treatment of heavy metals wastewater with high concentration of sulfate, and to better understand the mechanism of calcium sulfate scale formation, the equilibrium solubility data of CaSOa-Ca（OH）2-H2O system at 298.15 K were theoretically calculated via the Pitzer semi-empirical ion-interaction theory, and determined experimentally by the optical method combining with X-ray diffractometry, and the calculated and determined phase diagrams of CaSOa-Ca（OH）2-H2O system were plotted and compared. Physical definition of each area was studied, and the physical law of characteristic point and line was explained in detail. Adjusting the pH value of neutralization-hydrolysis solution depended on the SO4z- concentration in the system. And interaction characteristics between the solubilities of CaSO4（s）and Ca（OH）2（s）were found out.
Sulfate adsorption by poly（m-phenylenediamine）s（PmPDs） with various oxidation states synthesized through chemically oxidative polymerization was investigated.Series of sorption experiments were conducted,and the adsorption mechanism and the relationship between oxidation state and adsorption performance were studied with the characterization of Fourier transform infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,pH tracking and energy calculation.The results show that the adsorption performance in acidic solution is improved with the decrease of oxidation state of poly（m-phenylenediamine）（PmPD）.The rate constant is as high as 425.5 mg/（g·min） in the short equilibrium time of 30 min.The estimated highest adsorptivity of sulfate ions is 95.1%.According to the Langmuir equation,the adsorbance is 108.5 mg/g.The sulfate desorption efficiency is about 95% and the accumulative adsorbance is up to 487.95 mg/g in 5 cycles.
An important filamentous industrial fungus,Rhizopus cohnii(R.cohnii),was used as an efficient biosorbent for removing cadmium from wastewater.The sorption conditions,such as pH,the dose of biomass and the initial concentration of cadmium were examined.Two kinds of adsorption models were applied to simulate the biosorption data.The uptake of cadmium was higher in weak acid condition than in strong acid condition.Nearly no sorption of cadmium occurred when the pH value was lower than 2.0. Biosorption isothermal data could be well simulated by both Langmuir and Freundlich models.Langmuir simulation of the biosorption showed that the maximum uptake of cadmium was 40.5 mg/g(0.36 mmol/g)in the optimal conditions,which was higher than many other adsorbents,including biosorbents and activated carbon.In addition,the reusability results showed that after five times of sorption and desorption process,the sorption capacity of R.cohnii could still maintain nearly 80%,confirming its practical application in cadmium treatment.Fourier transform infrared spectrum revealed that carboxyl,amino and hydroxyl groups on biosorbent R.cohnii surface were responsible for the biosorption of cadmium.
A total of 153 soil samples were collected from Changsha City, China, to analyze the contents of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn. A combination of sampling data, multivariate statistical method, geostatistical analysis, direct exposure method and triangulated irregular network （TIN） model was successfully employed to discriminate sources, simulate spatial distributions and evaluate children＇s health risks of heavy metals in soils. The results show that not all sites in Changsha city may be suitable for living without remediation. About 9.0% of the study area provided a hazard index （HI）1.0, and 1.9% had an HI2.0. Most high HIs were located in the southern and western areas. The element of arsenic and the pathway of soil ingestion were the largest contribution to potential health risks for children. This study indicates that we should attach great importance to the direct soil heavy metals exposure for children＇s health.
