Arsenic removal from aqueous solutions by adsorption on red mud

Use of red mud, which is a waste product from bauxite processing, has been explored as an alternate adsorbent for arsenic in this study. The tests showed that the alkaline aqueous medium (pH 9.5) favored the removal of As(III), whereas the pH range from 1.1 to 3.2 was effective for As(V) removal. The process of arsenic adsorption follows a first-order rate expression and obeys the Langmuir's model. It was found that the adsorption of As(III) was exothermic, whereas As(V) adsorption was endothermic. It would be advantageous to use this residue as an adsorbent replacing polyvalent metal salts.     

Mercury removal from aqueous solutions by zinc cementation

The main purpose of this research is to study the addition effect of the surfactant and other operating factors on the treatment of wastewater containing mercury ions in aqueous solution by cementation with sacrificing metal, zinc. The removal of mercury ions from aqueous solutions by cementation of zinc powder was found to be a function of solution pH and temperature, amount of zinc, concentration of mercury ion, contact time and the addition of several organic surfactants. Cementation of mercury was shown to be a feasible process to achieve a very high degree of mercury removal over a broad operational range within a fairly reasonable contact time. The reaction rate is approximately first order with respect to the concentration of mercury ion in aqueous solution. Among the surfactants used in this study, only the presence of SDS, an anionic surfactant, slightly enhanced the cementation rate of mercury. The presence of CTAB and Triton-X100 retarded the cementation of mercury by zinc.     

Removal of ammonium and phosphates from aqueous solutions by biochar produced from agricultural waste

The concern about protecting water quantity and quality is one of the most severe challenges of the twenty-first century since the demand for water resources grows as the population and its needs grow. Additionally, and as expected, most human activities produce wastewater containing undesirable contaminants. On the other hand, the generation of agricultural waste and its inappropriate disposal causes further problems. Current wastewater treatment methods involve a combination of physical and chemical processes, technologies, and operations to remove pollutants from effluents; adsorption is an excellent example of an effective method for wastewater treatment, and biochar is currently one of the most valuable adsorbents. This review focuses on new research about applying biochar produced from agricultural waste as a low-cost and environmentally friendly method for removing ammonium and phosphates from aqueous solutions.

     

Removing cadmium from aqueous solutions utilizing agricultural wastes

The purpose of this study was to determine the cadmium (Cd) biosorption capacities of several agricultural wastes from aqueous solutions. Samples were tested unaltered and after hydrochloric acid treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the Cd solutions. Desorption studies were performed to determine if the removed Cd could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional Cd biosorption cycles. The results of this study demonstrate a wide range of Cd biosorption proficiencies ranging from 33 to 100% removal. The parameters that resulted in higher Cd removal include higher sample dose, higher pH, and lower Cd solution concentration. Desorption results showed a 36–56% Cd recovery rate. Reused AWS were effective at removing Cd during subsequent trials. Therefore, all AWS types tested in this study can be reused for additional Cd biosorption cycles. Hence, it is possible that using AWS for metal treatment could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each Cd biosorption cycle.     

Biosorption of copper from aqueous solutions utilizing agricultural wastes

The purpose of this study was to determine the copper (Cu) biosorption capacities of several agricultural wastes from aqueous solutions. Samples of agricultural wastes were tested unaltered and after hydrochloric acid (HCl) treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the Cu solutions. Desorption studies were performed to determine if the removed Cu could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional Cu biosorption cycles. The results of this study demonstrate a wide range of Cu biosorption proficiencies ranging from 0% to 100% removal. The parameters that resulted in higher Cu removal include higher pH and lower Cu solution concentration. Desorption results showed a 58% to 86% Cu recovery rate. Three of the five reused AWS were effective at removing Cu during subsequent trials. Therefore, these AWS types can be reused for additional Cu biosorption cycles. Hence, it is possible that using those AWS for metal treatment could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each Cu biosorption cycle.     

A case study of methomyl removal from aqueous solutions by four natural Albanian clays

This study evaluated the adsorption properties of four Albanian natural clays from the regions of Brari, Currila, Dardha, and Prrenjasi for commercial methomyl from aqueous solutions. Three methomyl concentrations, 0.200, 0.400, and 0.600 mg/ml, were tested at 25°C to study the influence of the insecticide concentration on the adsorption process for each natural clay type. Within 48 hr of contact time, the adsorption pathways of methomyl on the selected clays are well described by a Langmuir‐like adsorption kinetic model and an intraparticle diffusion model. Hydrolysis and desorption inhibit the overall removal process. The increase of methomyl concentration in solution within the first 48 hr leads to linear adsorption increases well described by Langmuir and Freundlich adsorption isotherms and disfavors the desorption step for the Brari, Currila, and Dardha clays. For the methomyl concentration of 0.600 mg/ml, within 24 hr of contact time, the Dardha and Prrenjasi clays reveal 1.471 and 1.956 mg/g methomyl uptake, respectively. The Brari and Currila clays show longer saturation times followed by better methomyl retention. The Dardha and Prrenjasi clays exhibit fast and high adsorption combined with low retention times.     

Utilizing agricultural wastes to remove hexavalent chromium from aqueous solutions

The purpose of this study was to determine the hexavalent chromium (Cr^VI) biosorption capacities of several agricultural wastes from aqueous solutions. Samples were tested unaltered and after hydrochloric acid (HCl) treatment. Additional parameters tested include sample dose, contact time, particle size, mixing temperature, and the concentrations and pH of the Cr^VI solutions. Desorption studies were performed to determine if the removed Cr^VI could be recovered. In addition, tests were conducted to determine if the agricultural waste samples (AWS) could be reused for additional Cr^VI biosorption cycles. The results of this study demonstrate a wide range of Cr^VI biosorption proficiencies ranging from 13 to 98 percent removal. The parameters that resulted in higher Cr^VI removal include HCl treatment, higher sample dose, lower Cr^VI solution concentration, and lower mixing temperature. Desorption results showed an 8 to 25 percent Cr^VI recovery rate. Reused AWS were effective at removing Cr^VI during subsequent trials. Therefore, all AWS can be reused for additional Cr^VI biosorption cycles. Hence, these could reduce hazardous waste disposal inefficiencies and costs by avoiding disposing of spent AWS following each Cr^VI biosorption cycle.     

赤泥中重金属元素的浸出性与结合形态

采用等离子体质谱仪分析了拜耳法赤泥(BRM)和烧结法赤泥(SRM)中Cr,Ni,Cu,Zn,As,Cd,Cs,Pb等8种重金属元素的含量。采用逐级提取的方法分析了BRM和SRM中8种重金属元素的浸出情况和形态分布差异。实验结果表明:SRM中水溶态As的质量浓度达到17.3μg/L,BRM和SRM中可交换态Cr的质量浓度均在2 300μg/L以上,对水环境可能存在潜在危害;两种赤泥中不同形态重金属的浸出率有较大差异,SRM中Ni和BRM中Zn的总浸出率分别在60%和50%以上。     

活性炭吸附缓冲非稳态VOCs研究进展

活性炭类吸附剂可以有效地缓冲挥发性有机物(VOCs)的浓度负荷波动。综述了活性炭对非稳态VOCs吸附缓冲的作用原理及类型,从吸附剂、吸附质、进气性质和设备及操作条件等方面讨论了影响吸附缓冲性能的因素,并对今后该领域的研究方向提出了展望。指出:应当进一步研究吸附剂和吸附质的交互作用、波动负荷的影响以及VOCs在活性炭中的迁移扩散现象;同时,通过深层次的实验测试和模型模拟为反应器的设计和操作参数的估算提供指导。     

ACF床动态吸附及脱附性能试验研究

利用活性炭纤维(ACF)床在热态下进行动态吸附及脱附性能试验,研究了W/Q、水蒸汽含量对ACF吸附性能的影响,并利用ACF的选择性吸附性能,采用分段吸附,以达到同时高效吸附SO2和NOx.对ACF床进行了水洗脱附与负吸热空气法脱附试验.     

Immobilization of copper flotation waste using red mud and clinoptilolite

The flash smelting process has been used in the copper industry for a number of years and has replaced most of the reverberatory applications, known as conventional copper smelting processes. Copper smelters produce large amounts of copper slag or copper flotation waste and the dumping of these quantities of copper slag causes economic, environmental and space problems. The aim of this study was to perform a laboratory investigation to assess the feasibility of immobilizing the heavy metals contained in copper flotation waste. For this purpose, samples of copper flotation waste were immobilized with relatively small proportions of red mud and large proportions of clinoptilolite. The results of laboratory leaching demonstrate that addition of red mud and clinoptilolite to the copper flotation waste drastically reduced the heavy metal content in the effluent and the red mud performed better than clinoptilolite. This study also compared the leaching behaviour of metals in copper flotation waste by short-time extraction tests such as the toxicity characteristic leaching procedure (TCLP), deionized water (DI) and field leach test (FLT). The results of leach tests showed that the results of the FLT and DI methods were close and generally lower than those of the TCLP methods.     

A study of iron mineral transformation to reduce red mud tailings

This study examines the effects of iron mineral transformation in an aluminum extraction process on the settling behavior, and the physical and chemical properties of the resulting red mud slurry that must be disposed of. By producing a red mud with a higher solid content, the total volume of mud slurry will also be reduced for a given alumina production rate and more caustic soda will be recovered. The settling behavior and the mineralogical, physical, and physico-chemical properties of one bauxite and three red muds processed under varying conditions were analyzed based on examination of the iron mineral transformations. The properties of red muds derived from the same bauxite can differ markedly due to variations in operating conditions of the Bayer process, such as temperature and the addition of a reducing agent. The settling of red mud can be improved by converting goethite into hematite and/or magnetite to produce a mud of larger particle size, smaller specific surface area, and larger specific gravity, characteristics which reduce the total volume of mud slurry to be disposed of and which allow for less potential contamination from caustic soda. This study also found that the by-product--Bayer sodalite--has the high exchange capacity for Na+ that might contribute to the long-term environmental problems.     

CaCl_2废液在赤泥脱碱中的应用

采用CaCl_2废液对赤泥进行脱碱处理。分析了脱碱机理,考察了CaCl_2废液对赤泥进行脱碱处理的影响因素。研究结果表明,在赤泥加入量为5 g、CaCl_2废液加入量为4 m L、反应温度为80℃、反应时间为4 h的最佳条件下,Na去除率达75%,脱碱后赤泥中Na的质量分数低于0.8%,脱碱后CaCl_2废液的p H约为7。CaCl_2废液对赤泥进行脱碱处理的脱碱机理为CaCl_2废液中的CaCl_2、Mg Cl2和酸与赤泥中的碱发生离子交换反应,使得赤泥中的Na转化为Na Cl,进入到溶液中,从而脱除赤泥中的碱。     

氯化物浸泡活性炭对汞的吸附特性研究

用氯化锌溶液对活性炭(AC)颗粒进行浸泡，研究其在低温下对气态汞的吸附特性。结果表明，活性炭对汞的吸附与活性炭特性、试验温度、反应时间、浸泡液浓度等因素有关。     

Pore structure and adsorption properties of activated carbon prepared from granular molded waste paper

We have previously manufactured activated carbon using waste paper board, which was prepared by adding 8% phenol resin adhesive to torn waste newspaper and hot-pressing. In this study, the pretreatment process of the raw material was simplified; the waste paper was extruded to form granules. The activated carbon was manufactured by the carbon dioxide activation method using the granules as the raw material. The properties of the activated carbon were evaluated based on the pore structure, the iodine adsorption number, and the adsorption of toluene vapor in a sealed chamber. The activated carbon, which was manufactured at an activation temperature of 1100°C and a treatment time of 60min, exhibited a specific surface area of 1241m²/g and an iodine adsorption number of 1120mg/g. These results were similar to those obtained for two commercially available activated carbons. The extent of toluene vapor adsorption by this activated carbon was similar to that observed for the two commercial activated carbons over a period of 130min.     

城市污泥制备水中重金属吸附剂及其吸附特性研究

本实验利用城市污水厂的脱水污泥,通过化学活化法制备活性炭.研究活化温度、活化时间、固液比和活化剂浓度等因素对制备污泥活性炭的影响,确定氯化锌法制备污泥活性炭的最佳工艺为活化温度550 ℃、活化时间30 min、固液比1∶2、氯化剂浓度45％.将制备的污泥活性炭吸附Cu2＋,Cr6＋,Cd2＋3种重金属离子模拟废水,研究pH值、吸附时间、污泥投加量、温度等因素对吸附过程的影响.实验结果表明,剩余污泥对Cu2＋,Cr6＋,Cd2＋3种重金属离子都具有良好的吸附效果,在优化条件下,3种重金属离子去除率分别达到94％,76％,81％,吸附能力大小顺序为Cu2＋＞Cd2＋＞＋Cr6＋.     

Optimizing Cr(VI) adsorption on activated carbon produced from heavy oil fly ash

In order to explore the beneficial utilization of heavy oil fly ash (HOFA) generated in the power plants, the present study is intended to optimize the chromium(VI) [Cr(VI)] adsorption on activated carbon produced from HOFA. The raw HOFA obtained from a power plant was washed by nitric/hydrochloric acid and activated at 800 °C with a holding time of 60 min to produce fly ash activated carbon (FAC). Phosphoric acid was used as a chemical agent to improve the surface characteristics of the HOFA during the activation process. Batch adsorption experiments were employed to evaluate the effects of different parameters such as initial Cr(VI) concentration, pH, and FAC dose on the removal of Cr(VI) from aqueous solution. A total of 17 adsorption experimental runs were carried out employing the detailed conditions followed the response surface methodology based on the Box–Behnken design. The results indicate that developed FAC has the potential for removing Cr(VI) from wastewater. Under the test conditions, a maximum of 91.51 % Cr(VI) removal efficiency was achieved.     

催化臭氧氧化—生物活性炭吸附组合工艺处理反渗透浓水

采用催化臭氧氧化—生物活性炭吸附组合工艺处理反渗透(RO)浓水,比较了4种催化剂催化臭氧氧化的性能,优化了初始RO浓水pH、臭氧氧化时间、生物活性炭柱空床停留时间(EBRT)等工艺条件。实验结果表明:以WP-01为催化剂催化臭氧氧化RO浓水时无需调节废水pH;臭氧氧化反应5 min时RO浓水的BOD5/COD达0.28,可生化性得到显著改善;WP-01催化剂重复使用30次其催化活性没有明显下降;生物活性炭吸附单元的EBRT控制在30 min左右,可确保出水COD稳定在50 mg/L以下,符合GB 18918—2002《城镇污水处理厂污染物排放标准》的一级A标准;催化臭氧单元处理每吨RO浓水的电费约为1.22元。     

Hidden values in bauxite residue (red mud): Recovery of metals

Bauxite residue (red mud) is a hazardous waste generated from alumina refining industries. Unless managed properly, red mud poses significant risks to the local environment due to its extreme alkalinity and its potential impacts on surface and ground water quality. The ever-increasing generation of red mud poses significant challenges to the aluminium industries from management perspectives given the low proportion that are currently being utilized beneficially. Red mud, in most cases, contains elevated concentrations of iron in addition to aluminium, titanium, sodium and valuable rare earth elements. Given the scarcity of iron supply globally, the iron content of red mud has attracted increasing research interest. This paper presents a critical overview of the current techniques employed for iron recovery from red mud. Information on the recovery of other valuable metals is also reviewed to provide an insight into the full potential usage of red mud as an economic resource rather than a waste. Traditional hydrometallurgy and pyrometallurgy are being investigated continuously. However, in this review several new techniques are introduced that consider the process of iron recovery from red mud. An integrated process which can achieve multiple additional values from red mud is much preferred over the single process methods. The information provided here should help to improve the future management and utilization of red mud.