Fixation of Heavy Metals in Clay and Sludge under Elevated Temperatures and Pressures

Abstract

The retention of heavy metal by clay minerals has been thoroughly studied. The smectic types, in particular montmorilkmite. have a large capacity of cation exchange, a property which can be related to their structure. The experiments in this work were carried out with bentonite, a clay with a high content of montmorillonite. Its capacity for absorption of different metals was shown to decrease in the order Cu > Zn > Ni > Cd

Laboratory work was carried out with equipment simulating a continuous pipe autoclave. Reaction time was typically 30?min and the temperature could be varied up to279°C. After the treatment, leaching tests were performed at pH 5 and 3. It was shown that the fixation increased with temperature and with the amount of added Na₂CO₃ or NaHCO₃, the effect of the former being slightly greater than the latter. The order of retention was Ni > Cu > Zn > Cd. Only 1.2% of nickel but 35% of cadmium are leached under the same conditions (H₂SO₄ at pH 3.0-3.1). This probably reflects the adaptation of the ion to the silicate lattice. By substituting Ca(OH)₂ for Na₂CO₃, the ability to retain heavy metals became neutralized during the autoclave treatment. This is again ascribed to the thorough conversion of the montmorillonite structure by reaction with Ca(OH)₂

Many soils contain smectic clay minerals in amounts sufficient to ensure fixation by direct autoclaving. In other cases such as industrial waste or municipal sludge, it is necessary to add an adequate clay. Cadmium as one of the most hazardous pollutants is not satisfactorily fixed by silicate lattices. In such a case, a more promising approach is transforming the pollutant into sulphide which can be done hydrothermally in the autoclave by adding a small amount of sulphur under anoxic conditions. The case for disposing sulphide-bound metals to the environment under oxidizing conditions presents problems. The problem is that the ubiquitous thiobacilli will start to convert the sulphides into more or less soluble sulphates when the oxygen pressure is sufficient. Therefore, dumping sites must be chosen with special reference to long term anoxic conditions.     

Recovery and Marine Clay Stabilization of Heavy Metals Present in Spent Hydrotreating Catalysts

This paper presents the results of an investigation on the treatment of two industrial solid wastes produced by oil refineries in Singapore, namely Ni∕Mo∕γAl2O3 and Co∕Mo∕γAl2O3. Calcination at 500°C was effective in removing carbon and sulfur in both wastes followed by generation of heavy metal oxides. A two-stage leaching process was successful in removing 44% nickel, 77% cobalt, and 83% molybdenum. However, toxicity characteristic leaching procedure leaching tests for spent catalyst residues of Co∕Mo∕γAl2O3 and Ni∕Mo∕γAl2O3 after the two-stage leaching process showed that the concentration of Mo, Co, and Ni in the leachate exceeded the allowable limits. Finally, the residues, when subjected to an enhanced binder stabilization treatment with marine clay, produced a commercial-value brick made of up to 30% by weight spent catalysts. It is believed that stabilization can be achieved through either encapsulation whereby the clay forms a matrix around the heavy metals to prevent leaching or incorporation in which the heavy metals actually become part of the stabilizing matrix.     

Numerical Simulation of Vertical Pullout of Plate Anchors in Clay

The behavior of strip and circular plate anchors during vertical pullout in uniform and normally consolidated clays was studied in this paper by means of small strain and large deformation finite-element analyses. Both fully bonded (attached), and “vented” (no suction on rear face), anchors were considered. The current numerical results were compared with existing laboratory test data, finite-element results, and analytical solutions. This study showed that, in small strain analysis, the scatter of existing data was mainly due to the effect of soil stiffness. In large deformation analysis, when soil and anchor base were attached with suction, the pullout capacity factor formed a unique curve independent of the soil strength (su), soil effective unit weight (γ′) and anchor size (B=width of strip anchor and D=diameter of circular anchor). The transitional embedment depth ratio, HSD/B or HSD/D, (where HSD=transition depth between shallow and deep embedment) was 1.4 for a strip anchor and 0.75 for a circular anchor. The ultimate pullout capacity factors (Nc) for deep embedment were 11.6 and 11.7 for smooth and rough strip anchors and 13.1 and 13.7 for smooth and rough circular anchors, respectively. However, when the anchor base was vented, the soil stayed attached to the anchor base for deep embedment, and the pullout capacity was therefore the same as for the attached anchor. The separation depth ratio, Hs/B or Hs/D, (where Hs=embedment depth at which the soil and anchor base separated) was found to increase linearly with the normalized strength ratio, su/γ′B or su/γ′D.     

金属凝固微观组织数值模拟研究进展

综述了金属凝固微观组织数值模拟研究在国内外的研究进展，阐述了该研究领域主要采用三种模拟方法（确定性方法，随机性方法，相场方法），并着重介绍了最新的改进单元自动控制法（MCA法）的求解和模拟过程，指出了该研究领域目前存在的问题及今后的发展方向。     

Numerical Simulation of Heat Transfer in Porous Metals for Cooling Applications

Porous metals have low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Hence, they have attracted a large amount of interest over the last few decades. One of their applications is for thermal management in the electronics industry because of their fluid permeability and thermal conductivity. The heat transfer capability is achieved by the interaction between the internal channels within the porous metal and the coolant flowing through them. This paper studies the fluid flow and heat transfer in open-cell porous metals manufactured by space holder methods by numerical simulation using software ANSYS Fluent. A 3D geometric model of the porous structure was created based on the face-centered-cubic arrangement of spheres linked by cylinders. This model allows for different combinations of pore parameters including a wide range of porosity (50 to 80 pct), pore size (400 to 1000 µm), and metal particle size (10 to 75 µm). In this study, water was used as the coolant and copper was selected as the metal matrix. The flow rate was varied in the Darcian and Forchheimer’s regimes. The permeability, form drag coefficient, and heat transfer coefficient were calculated under a range of conditions. The numerical results showed that permeability increased whereas the form drag coefficient decreased with porosity. Both permeability and form drag coefficient increased with pore size. Increasing flow rate and decreasing porosity led to better heat transfer performance.     

微生物在土壤中迁移实验与数值模拟

A thorough understanding of bacteria transport in soil and groundwater is vital to the successful practice of environmental bioremediation. In this work, a dual-process adsorption with growth and decay model of bacterial transport was proposed. The on-site soil and the high efficiency methyl tert-butyl ether (MTBE) degrading bacterium Chryseobacterium sp.A-3, was used in the experiments. The model was validated using one-dimensional soil column experiments. The results show that the dual-process adsorption with growth and decay model proposed well describes the migration mechanism of microorganisms in soil and groundwater environment. According to the model analysis and simulation, the bacterial transport is enhanced as flow velocity and inlet cell concentration increase. Compared with the contaminant MTBE, the bacteria show stronger transport capacity but the irreversible straining in soil prevents the bacteria from transporting longer than MTBE. The results have certain instructive significance to the in-situ contamination remediation operation.     

Equivalent Effective Stress and Compressibility of Unsaturated Kaolinite Clay Subjected to Drying

Three-dimensional compressibility tests performed on unsaturated kaolinite clay subjected to drying showed that the volume change is a function of the equivalent effective stress (EES). The EES in the clay at different water contents was measured by performing direct tensile tests. When the clay has high water content (saturated funicular state), its volume decreases notably as the water content is reduced, i.e., the equivalent effective stress is increased. If the clay has a water content in an intermediate interval (complete pendular state), the volume is almost constant because the equivalent effective stress is almost constant. For the interval of low water contents (partial pendular state), the volume of the clay increases as the water content is reduced. This occurs because the equivalent effective stress is reduced when the moisture content in the clay is reduced, and contrasts with the saturated funicular state. The minimum volume in the clay was reached when the maximum equivalent effective stress was developed. A conceptual framework explains the influence of the different states of water distribution to the EES.     

钨合金变形微观力学行为的计算机数值模拟

提出了钨合金的组织结构模型.在此基础上通过有限元法对钨合金拉伸变形时组织结构中的应力分布及其变化规律进行了计算机数值模拟研究.结果表明：钨合金拉伸变形时拉伸方向最大正应力和最大Mises应力区域在钨颗粒相中,同时钨颗粒还将受到垂直于拉伸方向的压应力;最大剪切应力分布在粘结相中,随拉伸变形增加,粘结相最先进入塑性状态;由于粘结相的塑性变形,钨合金中应力不断重组,应力逐渐在钨颗粒中集中.     

稳定流与非稳定流情况下非饱和—饱和区域重金属运移模拟

为定量研究稳定流与非稳定流情况下非饱和带—饱和区域内水流及溶质迁移过程,在非饱和带及饱和区域流动理论及溶质运移理论基础上,建立了非饱和带—饱和区域内水流方程与污染物运移模型,采用Van Genuchten-Mualem模型来描述相对渗透率函数,基于Toughreact软件对模型进行模拟计算并给出模拟结果。模拟结果得出:在稳定流情况下,非饱和带及饱和区域流速均逐渐减小,最后趋于稳定;而非稳定流情况下,流速初始阶段逐渐减小,后期随着各季度降水量的不同流速大体呈周期性变化。在总降水量相同及其他条件相同的情况下,非稳定流相对于稳定流对溶质运移存在促进作用,即其运移速率更快,但影响尺度不大;随着时间的推移,污染物将透过包气带进入地下水中,其中钠离子最快,六价铬次之,铀出现最晚。     

富水软土地层地铁隧道开挖地层固结沉降数值模拟

为了对富水软土地层地铁隧道开挖引起的地层固结进行定量研究,考虑流固耦合效应和施工力学效应的综合作用,应用FLAC3D对降水、动态降水和非降水3种工法进行数值模拟的对比研究,分别得到了地表沉降和地层固结沉降曲面。研究结果表明,3种工法引起的地表沉降量分别为:非降水法29mm、动态降水法60mm和降水法116mm,它们的比值大致为1∶2∶4,地层固结沉降量占各自的整个地表沉降量的比率分别为:非降水法27%;动态降水法50%;降水法79%。显然,非降水法是在富水软土地层地铁隧道施工中控制地层固结沉降最有效的方法。计算结果与现场实测资料进行比较,两者十分接近。研究成果已成功地应用于深圳地铁工程中。     

钨合金力学行为的计算机数值模拟─—宏观力学性能

在微观力学行为分析的基础上,对90W合金宏观力学性能及其与微观结构因素（粘结相力学参数）之间的关系进行了计算机数值模拟研究.结果表明：钨合金性能与粘结相力学参数密切相关.随着粘结相弹性模量增加,合金的抗拉强度增加,但延伸率降低.当粘结相屈服强度800MPa时,合金抗拉强度随粘结相屈服强度增加而增大,在粘结相屈服度为800MPa时达到最大值.随粘结相抗拉强度增加,合金抗拉强度和延伸率均呈近似线性规律增加.合金延伸率对粘结相应变硬化模量极为敏感.     

大型钢锭加热过程数值模拟与验证

对重量为44t的大型钢锭的锻前加热过程进行了数值模拟分析.介绍了钢锭的结构尺寸、材料的热物性参数以及数值模拟所需的边界条件,模拟得到了加热过程中钢锭的升温曲线.在加热过程中对钢锭内部温度进行了测量,结果表明模拟结果与实测结果基本吻合.     

中厚板淬火过程的热力学数值模拟及实验

 以高密度管流冲击钢板表面时的对流换热边界为基础,采用ANSYS三维有限元对中厚板淬火中的钢板温度场、应力场及应变场进行了数值模拟,并对模拟得到的温度与时间、应力以及塑性应变的关系进行分析,得到了淬火冷却过程中保持钢板平直状态下应力、应变及变形的特点,为采用适当工艺措施使中厚板淬火获得平直板形提供了理论依据。     

污泥中重金属的回收工艺研究

研究了重金属污泥中的4种重金属离子(Cu2+、Zn2+、Pb2+、Cd2+)的回收方法,考察了酸的种类、酸浓度、温度、时间、固液比对浸出效果的影响。结果表明,4mol/L的HNO3与750℃焙烧3h后的污泥在固液比1∶20,转速600r/min,80℃下反应3h,Cu2+、Pb2+、Zn2+、Cd2+的浸出率分别为92.0%、99.5%、99.5%、99.3%。     

连铸过程中湍流传输和两相区凝固的数值模拟

综述了在连铸数值模拟过程中，为评估流体流动对铸坯热量传递和凝固过程影响所开发的有效导热模型和耦合模型。根据文献和用商业CFD软件计算的结果分析了在连铸湍流传输和两相区凝固的数值模拟过程中影响模型预测精确性的关键因素，包括有效导热模型中有效导热系数的确定、数值模拟模型的选取、湍流模型的应用、连铸坯凝固过程中湍流向层流的过渡、两相区流动中多孔介质的渗透率取值、固相分率与温度和成分的关系等，并给出选取合适模型参数的原则。     

重金属污染的危害与防治

论述了重金属污染的来源、特点、及对动植物特别是人类健康的危害．并简述了重金属污染的防治办法。     

厚板坯连铸结晶器流场数值模拟

针对鞍钢新轧钢第一炼钢厂厚板坯连铸结晶器建立了三维湍流数学模型和三维实体模型.应用有限元软件对厚板坯连铸结晶器内的流场进行了模拟,计算了铸机拉速、浸入式水口出口倾角和水口浸入深度等工艺参数对结晶器内钢液流动的影响.对比表明,数值模拟结果与水模实验结果相符.     

有色金属工业重金属废水重复利用综合技术分析

文章所研究的技术属于环境科学的重要研究领域,解决了有色金属工业重金属废水长期不能回用的技术难题,实现了废水在有色冶金生产过程各个工序中回用,使废水总回用率超过90％,循环水污垢热阻小于4．5×10^4m2·℃／W,污垢附着速度小于20mg／cm2·月,腐蚀速度小于5mg／dm2·d,现场测定阻垢缓蚀率大于98％。该技术的实施,减轻了环境污染,节约了水资源,推动了有色工业企业的环境保护与科技进步,具有显著的经济、环境与社会效益。     

Numerical Analysis of T-Bar Penetration in Soft Clay

The penetration resistance of a cylindrical T-bar penetrometer in soft clay is affected by features such as anisotropy, high strain rates, and gradual strain-softening during passage of the T-bar. In order to evaluate these effects, a detailed numerical study has been undertaken, comprising: (1) finite-element analysis; and (2) a strain path approach within the upper bound plasticity mechanism. These studies showed that the T-bar factor is relatively insensitive to the degree of strength anisotropy, provided the penetration resistance is normalized by the average shear strength. Strain rates were found to be six or seven orders of magnitude greater than typical laboratory testing rates, and about three orders of magnitude higher than in a standard vane test. However, the effect of high strain rates is partly compensated by remolding of the soil, where average strains of 400% are imposed on the soil. Charts are presented showing how the separate effects of high strain rates and partial softening may be combined to derive a T-bar factor for a given soil. The paper concludes with a discussion of the measurement of remolded shear strength using cyclic T-bar tests, and interpretation of the T-bar resistance in fully remolded soil.     

基于蒙特卡罗模拟的危险废物处置场地下水重金属健康风险评估

以重庆市危险废物处置场周边地下水为研究对象,测定了As、Cd、Al、Cu、Zn、Hg、Pb、Cr、Ni和Fe金属元素浓度,利用内梅罗指数法和地下水污染物容量评价指数法分析地下水重金属污染水平,并采用蒙特卡罗模拟的健康风险评价模型评估地下水中重金属的人体健康风险。结果表明,研究区地下水8月检出因子多于5月,超标情况主要集中在8月。内梅罗指数和地下水污染物容量指数表明,地下水中各重金属8月污染程度总体高于5月,Al为主要污染元素;5#点位污染程度最高,其他点位无污染。健康风险表明,非致癌健康风险儿童高于成人,非致癌健康风险的主要影响途径为饮用水途径;儿童和成人的致癌健康风险均在可接受范围内,但儿童的致癌健康风险高于成人。敏感性分析表明,非致癌风险中Al、Pb和每日平均饮用量(IR)的敏感度排前三,致癌风险中As的敏感度最高,Al和As是影响人体健康风险的主要因素。