Purification of heavy metal chromium in saturated sand by artificial freezing:Mechanism and method optimization

Heavy metal pollution of soil has become one of the most common hazards in human development.The artificial freezing method,especially the progressive freezing method,can reduce heavy metal pollutants in the soil and promises to be an effective in-situ treatment of contaminated sites.This study analyzes the freezing purification mechanism of heavy metal contaminants in saturated sand and identifies three main factors that impact the effects of purification:freezing rate,initial concentration,and diffusion coefficient.Moreover,one-dimensional freezing tests are carried out by different freezing modes.The experimental results show that the heavy metal chromium could only be removed effectively with a slow freezing rate.By optimizing the freezing mode and freezing rate,a long section of soil was frozen and purified,with the maximum purification rate reaching 65.8%.This study shows that it is feasible to treat contaminated saturated sand by a gradual-cooling freezing method.

Comparative Study of Removal of Hexavalent Chromium from Water Using Metal Oxide Nanoparticles

Hexavalent chromium is one of the important heavy metals found in water and wastewater. The hexavalent form of chromium is considered to be a human carcinogen because of its mutagenic and carcinogenic properties. This work has focused on the comparison of copper oxide nanoparticles and aluminium oxide nanoparticles for the removal of chromium(VI) from water. The cooper oxide nanoparticles (CuNP) and aluminium oxide nanoparticles (AlNP) were synthesised by sol gel method. Both the adsorbents were evaluated for the adsorption capacity using Langmuir and Freundlich adsorption model. The CuNP and AlNP were characterized for X-ray diffraction and SEM. The study indicated that the AlNP showed better removal as compared to CuNP and can be further explored as potential adsorbent for hexavalent chromium removal.

Thermodynamic Study on BaO－BaF_2－Fe_xO Slags Used for Dephosphorization of Chromium－Containing Hot Metal

Electrochemical measurements of the solid-oxide galvanic cell, Mo|Mo+MoO2|ZrO2 (MgO)| Fe+ (FexO)+Ag| Fe, have been made at temperatures of 1473K and 1573K in order to obtain the activities of FexO in BaO-BaF2-FexO slags used for dephosphorization of chromium-containing hot metal. The FexO activities show a significant dependence upon the molar ratio of BaO/BaF2. Within the homogeneous liquid region, the substitution of BaF2 for BaO has an effect of raising the FexO activity. From these activity data, the phase diagrams of the system BaO -BaF2-FexO are drawn at 1473K and 1573K. The temperature dependence of the activity coefficient of FexO at a fixed BaO/ BaF2 molar ratio can be expressed by formula RTlnγ(FexO)=constant.

Carburization of ferrochromium metals in chromium ore fines containing coal during voluminal reduction by microwave heating

Chromium ore fines containing coal (COFCC) can be rapidly heated by microwave to conduct the voluminal reduction, which lays a foundation of getting sponge ferrochromium powders with a lower content of C. Under the conditions of COFCC with n(O)-n(C) (molar ratio) as 1.00-0.84 and n(SiO2)-n(CaO) as 1.00-0.39, the samples were heated by 10 kW microwave power to reach the given temperatures and held for different times respectively. The results show that the low-C-Cr ferrochromium metal phase in the reduced materials forms before the high-C-Cr ferrochromium metal phase does. With increasing temperature the C content of ferrochromium metals is in a positive correlation with the content of Cr. The C content of ferrochromium metal in reduced materials is 0-10.07% with an average value of 4.68%. With the increase of holding time the Cr content in ferrochromium metals is in a negative correlation with the content of C, while the content of Fe changes in the contrary way. In the microwave field the kinetic conditions of carburization are closely related with the temperature of microwave heating, holding time and carbon fitting ratio.

2022年泰州市某区PM_(2.5)中金属元素含量测定及健康风险评价

目的分析2022年泰州市某区大气PM_(2.5)中金属元素的变化特征,评估其对人群的健康风险。方法2022年每月10—16日在监测点进行PM_(2.5)采样,采用电感耦合等离子体质谱法测定12种金属元素含量,利用富集因子(enrich factor,EF)法识别金属元素的来源,并进行人群健康风险评价。结果2022年泰州市某区大气PM_(2.5)中金属元素平均浓度由高到低为Mn>Pb>As>Se>Cr>Ni>Sb>Cd>Hg>Be>Tl,其中Al、Cd、Hg、Ni、Se、Tl浓度变化均有季节性差异(H值分别为13.932、11.817、15.836、8.423、7.876、14.316,P值圴<0.05);Cr、As、Sb、Cd等金属的EF值均>10。当人群暴露外环境时间达到3 h/d,Cr对成年男性、成年女性和儿童可能存在致癌风险;当暴露外环境中时间达到5 h/d,As对成年男性、成年女性可能存在致癌风险。结论该地区PM_(2.5)中金属元素主要来自于人为污染,季节性差异较为明显,Cr和As对人群的潜在健康风险较高,需引起重视。

某化工厂土壤与地下水Cr^(6+)污染分布及健康风险

为掌握某化工厂Cr^(6+)污染状况及风险水平,在研究区布设土壤与地下水采样点各19个,测定Cr^(6+)含量,分析污染特征与成因,并开展健康风险评估。结果表明:表层土壤(0~0.5 m)Cr^(6+)超标率为42.11%,其浓度随深度增加总体上降低,但在地下水位附近(15~20 m)回升,主要因长期淋溶作用使污染物向下迁移至含水层位富集。浅层地下水Cr^(6+)超标率为73.68%,深层地下水超标率为37.50%。整体而言该区土壤和地下水Cr^(6+)污染形势不容乐观,应开展水土协同治理。空间上表层土壤Cr^(6+)分布受人类活动影响,与投产期厂内功能区的划分相关性较低。地下水Cr^(6+)受水动力场影响,表现为西北高东南低,污染羽中心向下游方向迁移。土壤致癌风险均值为1.85×10^(-6),介于10^(-6)~10^(-4),风险中等,应引起必要重视。非致癌风险低于1,无慢性毒害影响。经口摄入土壤为主要暴露途径。地下水致癌风险高达10-2数量级,远超过10^(-4),风险不可接受。非致癌风险均值51.62,远大于1,极可能引发慢性毒害效应。另外需进一步考虑Cr^(6+)通过牛羊肉食物链进入人体的危害。

不同熔附金属对前牙烤瓷熔附金属全冠修复疗效

目的对比研究镍铬合金与金沉积对前牙烤瓷熔附金属(porcelain-fused-to-metal crown,PFM)全冠修复患者的应用效果以及对龈沟液(gingival crevicular fluid,GCF)炎症因子的影响。方法选入2020年9月-2022年2月在本院接受前牙PFM全冠修复的患者86例(86颗牙),根据修复材料不同分为镍铬合金组和金沉积组,每组43例(43颗牙)。比较两组的治疗效果、GCF炎症因子水平等指标。结果金沉积组修复体颜色、边缘密合度、边缘着色及继发龋均显著优于镍铬合金组(P<0.05),在修复体折裂瓷崩方面,两组无明显差异(P>0.05);修复6个月后,金沉积组GI、PD、GCF和GCF中TNF-α、IL-6、IL-1β和MMP-2水平水平均显著低于镍铬合金组(P<0.05);金沉积组满意度显著高于镍铬合金组(93.02%vs.74.42%,P<0.05)。结论镍铬合金与金沉积均是前牙PFM全冠修复的常用材料,而后者对患者局部牙周组织影响较小,在减轻GCF炎性因子水平、提高修复美观度及患者满意度方面优于前者。

乙二胺改性聚苯乙烯树脂对水体中铅(Ⅱ)、铬(Ⅵ)的吸附研究

采用乙二胺对氯甲基化聚苯乙烯树脂进行改性,利用改性后的树脂去除溶液中的铅(Ⅱ)和铬(Ⅵ)。通过改变pH、时间、浓度和吸附剂投加量,确定最佳吸附实验条件,得到改性后的树脂对铅(Ⅱ)和铬(Ⅵ)的最大吸附容量分别为119.60mg/g和128.28mg/g。动力学研究表明,该模型符合Langmuir模型。

污染土壤稳定化处理后铬返溶影响因子的研究

探究了稳定化处理后污染土壤中Cr的返溶影响因子。结果表明,对返溶释放促进作用最大的条件为:水淹、水溶液pH为1、40℃、一周鼓3 d氧气,这时土壤中Cr(VI)由10.00 mg/kg增至31.47 mg/kg,浸出液中总铬由0.15 mg/L增至0.36 mg/L。40℃、水淹、水溶液pH=1、水溶液pH=12、一周鼓3天氧气处理后Cr的有效态质量分数分别增加0.02%、1.46%、2.12%、0.03%、0.85%。含水率是影响污染土壤稳定化处理后Cr返溶的主要因素,pH为次要因素。在不同pH条件下,稳定化处理后的土壤中Cr的释放量皆与二级动力学方程拟合度最高。

光谱法测定农产品中铅镉铬汞砷的一次性消解方法

为了缩减检测用时与降低综合成本,对农产品中铅、镉、铬、汞、砷的检测方法进行改进,对检测条件进行优化和协调试验,探索一次性消解定容同时检测5种重金属元素的可行性。通过理论分析和试验研究,参考国标方法和成熟文献上的方法,消解用酸中加入盐酸和高氯酸,消解前120℃预消解30 min,消解赶酸后加入20 g/L硫脲+50 g/L抗坏血酸溶液转移定容,铅、镉检测加入磷酸二氢铵基体改进剂,砷、汞同时检测。通过条件取舍与优化,达到使用原子吸收(AAS)和原子荧光(AFS)同时检测的目的。检测标准物质和标准溶液,测定值均在其1倍不确定度范围内,准确度良好,相对标准偏差均小于20%,精密度良好。改进方法检测结果较准确,操作简便,适用于利用AAS和AFS对农产品中铅、镉、铬、汞、砷的测定。

煤基半焦对重金属土壤中铬和镉的原位钝化及作用机制分析

工业化和城市化的快速发展对土壤造成严重的重金属污染,其中由于铬、镉的毒性强,对环境的危害极大。以资源丰富的石河子煤和乌鲁木齐煤为原料经热解制得半焦,将其作为铬和镉污染土壤的钝化材料,以实现重金属污染土壤的修复和改良。利用热重分析得到两种煤样热解的特征温度;采用N_(2)等温吸附法对半焦的孔隙结构进行了表征。通过重金属浸提实验,研究了半焦钝化剂作用时间和添加量对单一污染土壤及复合污染土壤中重金属有效态含量的影响。结果表明:乌鲁木齐煤基半焦具有较适宜重金属钝化的表面特征,孔径主要集中在1.8 nm~4.0 nm,单位面积酸性官能团和碱性官能团数量较多,分别为0.0026 mmol/m^(2)和0.0164 mmol/m^(2);在其添加量为5%,粒径为300μm~500μm,与土壤作用时间为90 d的条件下,铬和镉的有效态含量分别下降了78%和21%。相比于单一污染土壤,竞争作用使得复合污染土壤中铬和镉的钝化效果略有下降。此外,土壤中添加半焦后,土壤的pH值保持在稳定的弱碱性范围内,其有机质含量和阳离子交换量均有提高,改善了土壤的理化性质,可增强土壤肥力。

Association between Plasma Metal Levels and Diabetes Risk： a Case-control Study in China

Objective Many metals, some of which have been classified as environmental endocrine disruptors, are used extensively in everyday consumer products and are ubiquitous in our living environment. In the present study, we aimed to explore the associations between the prevalence risk of type 2 diabetes and plasma levels of 20 trace elements as well as those of heavy metals in a Han Chinese population. Methods We conducted a case-control study to investigate the associations between plasma concentrations of 20 metals and diabetes in Jiangsu province. A total of 122 newly diagnosed cases of type 2 diabetes and 429 matched controls were recruited from community physical examinations in Suzhou City of Jiangsu Province. Plasma metal levels were measured by inductively-coupled plasma mass spectrometry. Results After adjusting for confounders, plasma vanadium, chromium, manganese, copper, zinc, arsenic, selenium, strontium, palladium, cadmium, cesium, and barium were associated with diabetes risk （P 〈 0.05）. The adjusted OR increased with increasing concentration of vanadium, manganese, copper, zinc, and cesium. Conclusion Many metals, including manganese, copper, zinc, arsenic, selenium, and cadmium in plasma, are associated with the morbidity of diabetes. Monitoring of environmental metal levels and further studies are urgently needed.

Effects of smelting parameters on the slag/metal separation behaviors of Hongge vanadium-bearing titanomagnetite metallized pellets obtained from the gas-based direct reduction process

Smelting separations of Hongge vanadium-bearing titanomagnetite metallized pellets（HVTMP）prepared by gas-based direct reduction were investigated,and the effects of smelting parameters on the slag/metal separation behaviors were analyzed.Relevant mechanisms were elucidated using X-ray diffraction analysis,FACTSAGE 7.0 calculations,and scanning electron microscopy observations.The results show that,when the smelting temperature,time,and C/O ratio are increased,the recoveries of V and Cr of HVTMP in pig iron are improved,the recovery of Fe initially increases and subsequently decreases,and the recovery of Ti O_2 in slag decreases.When the smelting Ca O/Si O_2 ratio is increased,the recoveries of Fe,V,and Cr in pig iron increase and the recovery of Ti O_2 in slag initially increases and subsequently decreases.The appropriate smelting separation parameters for HVTMP are as follows：smelting temperature of 1873 K;smelting time of 30–50 min;C/O ratio of 1.25;and Ca O/Si O_2 ratio of 0.50.With these optimized parameters（smelting time：30 min）,the recoveries of Fe,V,Cr,and Ti O_2 are 99.5%,91.24%,92.41%,and 94.86%,respectively.

Heavy Metal Accumulation in Medicinal Plants Collected from Environmentally Different Sites

Objective To estimate the heavy metal content in soil and selected medicinal plants procured from environmentally different sites of the same city. Methods Soil and plant samples of Abutilon indicum, Calotropis procera, Euphorbia hirta, Peristrophe bycaliculata, and Tinospora cordifolia were collected from 3 environmentally different sites of the city： heavy traffic area （HTA）, industrial area （IA）, and residential area （RA）. Pb by inductively coupled plasma emission spectrometry and compared Cd, Cr, and Ni were estimated in soil and plant samples Results The level of heavy metal was higher in soil than in plant parts studied. Accumulation of heavy metals varied from plant to plant. Pb was the highest in Calotropis procera root from HTA site and the lowest in Peristrophe bycaliculata whole plant from IA site. It was also lower in residential area than in heavy traffic area. Conclusion The level of heavy metal content differed in the same medicinal plant collected from environmentally different sites of the same city. Thus, it reiterates our belief that every medicinal plant sample should be tested for contaminant load before processing it further for medication.

Toxic hexavalent chromium reduction by Bacillus pumilis,Cellulosimicrobium cellulans and Exiguobacterium

Three bacterial strains B acillus pumilis,Cellulosimicrobium cellulans and Exiguobacterium were investigated when grown in Luria-Bertani(LB) medium at 500 μg/m L Cr(VI). The hexavalent chromium reduction was measured by growing the strains in De Leo and Ehrlich(1994) medium at 200 and 400 μg/m L K 2 Cr O 4. The optimal Cr(VI) reduction by strains B. pumilis,Exigubacterium and C. cellulans was 51%,39%,and 41%,respectively,at an initial K2 Cr O 4 concentration of 200 μg/m L at p H 3 and temperature 37°C. At an initial chromate concentration of 400 μg/m L,the Cr(VI) reduction by strains B. pumilis,Exigubacterium and C. cellulans was 24%,19%,and 18%,respectively at p H 3 at 37°C after 24 h. These strains have ability to reduce toxic hexavalent chromium to the less mobile trivalent chromium at a wide range of different environmental conditions and can be useful for the treatment of contaminated wastewater and soils.

Effect of potassium on as-cast microstructure of a hypereutectic high chromium cast iron

The present work mainly evaluates the effect of potassium(K) on as-cast microstructure of a hypereutectic high chromium cast iron by means of a field emission scanning electron microscope(FESEM) and an X-ray diffractometer using CuKα radiation with a 2θ range of 30-130°.Results showed that,with the addition of K-containing modifier,the large lath-like and/or rod-like primary M7C3 carbides can be modified to the hexagonal prisms,and the eutectic carbides can also be refined.In addition,the carbides are distributed much more homogeneously in the matrix.The modification effect of K is due to its aggregation at the liquid-solid interface and the adsorption on the relatively fast growing planes during the solidification,which influence the growth rates of different crystal planes and lead to the modification of the carbides.

Optimization of Chromate Reduction by Whole Cells of <i>Arthrobacter</i>sp. SUK 1205 Isolated from Metalliferous Chromite Mine Environment

Arthrobacter sp. SUK 1205 isolated from metalliferous chromite mine environment of Orissa, India showed wide degree of tolerance to heavy metals including Cr(VI), variety of antibiotics and was also capable of reducing Cr(VI) during growth. Freshly grown whole cells of this bacterium were evaluated for chromate reduction under batch culture using Vogel Bonner (V. B.) broth as the base. Cells of SUK 1205 were capable of completely reducing 100 μM Cr(VI) in V. B. broth within 48 h of incubation. Reduction of chromate increased with increase in cell density which attained maximum at 1010 cells/ml, however, reverse was the phenomenon when the concentration of Cr(VI) increased gradually. Glycerol, glycine and glucose promoted chromate reduction efficiency of the cells when used as electron donors. Optimum pH and temperature were found to be 7.0 and 35°C respectively. The process of reduction was inhibited by Ni(II), Mn(II), Zn(II) and Co(II), but Cu(II) and Fe(III) was promotive in nature. On the other hand, 2, 4-dinitrophenol was found to be neither promotive nor inhibitory for the reduction process, but carbonyl cyanide-m-chloro phenyl hydrazone, sodium azide, sodium fluoride and N,N,-dicyclohexyl carboiimide were inhibitory. Cells of SUK 1205 when permeabilized with toluene, triton X-100 and tween 80 showed an enhancement of the process and thereby indicated that reduction of Cr(VI) was mainly associated with soluble component of the cells. Arthrobacter sp. SUK 1205, therefore, showed great promise for use in Cr(VI) detoxification under a wide range of environmental conditions.

Effect of Rare Earth Elements on Thermal Fatigue Property of Low Chromium Semi-Steel

The effect of rare earth elements on eutectic carbide′s morphology of low chromium semi steel in as cast state and after heat treatment was investigated, and accordingly, the thermal fatigue property of this material was studied. The results show that RE can improve the eutectic carbide′s morphology, inhibit the formation and propagation of thermal fatigue cracks, therefore, promote the thermal fatigue property, which is more noticeable in case of the RE modification in combination with heat treatment. The optimal thermal fatigue property can be obtained when treated with 0.2% RE modification as well as normalization at 950 ℃ for 3 h.

Removal of heavy metals（Cr^（6＋），Ni^（2＋）） from polluted water using decaying leaves of plane（Plantanus orientalis）

plane decaying leaves have been found capable of removing chromium and nickel ions from aqueous solutions. The removal efficiency depends upon the pH conditions, ions components and concentrations, and concentrations of leaves in media. The maximum removal for unique Cr6+ is about 7.5-8.0g/kg leaves at pH 4. 0, for unique Ni2+ about 2. 6g/kg at the region of PH5. 0-5.5. Under the described conditions nickel increases chromium uptake by plane decaying leaves from solution.

Simultaneous Removal of Chromium and Lead from Water by Sorption on Iraqi Montmorillonite

A certified clay mineral from Iraq, montmorillonite, is used for the adsorption of chromium and lead ions from water. Experimental design is utilized here to plan for the practical work and analysis of the results. Batch wise experiments are carried out to equilibrate Cr and Pb solutions (250 mg/L) individually and simultaneously with montmorillonite (5 - 20 g/L) at various pH ranges (2 - 7.5) for 10 - 60 minutes. The results indicate perfect fit with the model used. Chromium adsorption is sensitive to pH changes being high at neutral medium. Lead is almost independent of the pH of the solution. In nearly neutral medium, the sorption capacity of Cr is 21.4 and that of lead is 24.3 mg/g. The optimum conditions for >96% Cr removal are 12 - 15 g clay/L, 40 - 50 minutes and a pH of 5 - 7. For lead, almost 100% removal can be attained using 12 - 15 g clay/L, 40 - 50 min. at a pH of 4 - 6. The effects of various operating parameters are discussed. Simultaneously, the lead shows a greater tendency to sorption than chromium and a ratio of 5:4 can best represent the occupation of the active surface of the clay. The most favorable conditions for simultaneous removing of Cr, 86% and Pb, 100% may be 12.5 g/L clay content and a pH of 7.5 within 30 minutes. The kinetic study of the results indicates the adsorption follow pseudo-second order kinetics in which chemical interaction is also involved. The kinetic study confirms the dependence of chromium adsorption on the pH of the medium being favoured at high pH values.