Leaching Behaviors of Arsenic from Arsenic-Iron Hydroxide Sludge during TCLP

The toxicity characteristic leaching procedure (TCLP) is normally used to evaluate if sludge should be managed as hazardous waste. This study examines immobilization mechanisms of arsenic onto arsenic-iron hydroxide sludge, the byproduct of arsenic removal by coagulation with ferric chloride. The leaching mechanism of arsenic from the sludge due to the TCLP is also investigated. Microscopic characterization techniques including scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) were employed to characterize the sludge samples with the As-to-Fe ratios of 0.07 to 0.15 before and after the TCLP. SEM-EDS and FT-IR results suggested that arsenic-iron hydroxide sludge be ferric hydroxide, whose surface is inner or outer spherically sorbed by arsenic, rather than the precipitate of insoluble iron-arsenic compounds such as Fe(AsO)4. This is also confirmed by XRD results, which revealed that none of such crystalline iron-arsenic compounds were detected in the arsenic-iron hydroxide sludge. Therefore, adsorption among other possible arsenic immobilization mechanisms, namely, precipitation, coprecipitation, and occlusion, is supposed to play the major role. Due to the TCLP, the arsenic concentrations ranging from 0.26 to 2.54?mg/L were leached out of the sludge samples with the As-to-Fe ratios ranging from 0.07 to 0.15, respectively. The changes of FT-IR patterns of the sludge after the TCLP suggested that during the TCLP, desorption and resorption of arsenic occurs. The relationship between arsenic in TCLP leachate and that remaining in the leached sludge can be modeled by Langmuir isotherm, an adsorption isotherm. This indicates that desorption and resorption of arsenic onto the leached sludge is the main phenomenon controlling arsenic leachability due to the TCLP.     

Bacterial Leaching of Metals from Tannery Sludge by Indigenous Sulphur-Oxidizing Bacteria—Effect of Sludge Solids Concentration

An investigation on the effect of sludge solids concentration on bioleaching of Cr(III) and other metals from tannery sludge by indigenous sulphur-oxidizing bacteria was carried out. The sludge solids concentrations ranged from 13 to 60 g/L. The concentration of elemental sulphur was fixed at 30 g/L. The results showed that the lowest pH reached after 25 days of bioleaching at all studied sludge solids concentration was about 1.3. The optimum sludge solids concentration for maximum metal leaching from tannery sludge was 40 g/L and about 87% of Cr(III), 73% of Al, 72% of Fe, 62% of Mg, and 73% of Zn could be leached in this case. During bioleaching, the concentrations of total and volatile suspended solids of the tannery sludge significantly decreased. The sulphur-oxidizing bacteria could tolerate a Cr(III) concentration as high as 5,930 mg/L at pH 1.3. The leaching efficiencies of Cr(III), Al, and Fe for both chemical leaching and bioleaching of tannery sludge were similar at pH 1.3. The leaching efficiency of Ca, Mg, and Zn in both leaching processes were identical for pH values in the range of 1.3 to 3.0.     

Bench-Scale Evaluation of Chemically Bonded Phosphate Ceramic Technology to Stabilize Mercury Waste Mixtures

This bench-scale study was conducted to evaluate the stabilization of mercury (Hg) and mercuric chloride-containing surrogate test materials by the chemically bonded phosphate ceramics technology. This study was performed as part of a U.S. EPA program to evaluate treatment and disposal alternatives to the current land disposal restriction (LDR) treatment standards for mercury. The stabilized materials were subjected to a suite of leaching tests: one test characterized the solubility and release behavior of mercury as a function of pH between the pH values of 2 and 12; the second test used the toxicity characteristic leaching procedure (TCLP); and the third leaching test used the TCLP “cage” modification. TCLP results showed that leachability of Hg decreased by approximately two orders of magnitude and a maximum of five orders of magnitude. The three leachability test methods produced similar amounts of leached mercury, but the test that studied mercury solubility as a function of pH released slightly higher levels (at pH 2) compared to the TCLP methods. On comparing the results obtained with the standard TCLP and the TCLP cage modification, we learned that the leachates from stabilized wastes containing 50 wt?% loading of elemental Hg and HgCl2 were within the LDR requirements. However, wastes containing higher loadings (i.e., 70 wt?% loading of Hg and HgCl2) had leachate concentrations exceeding the 0.2 mg/L treatment standard and therefore would not meet the Resource Conservation and Recovery Act disposal requirements.     

污泥炭田间老化对土壤重金属及养分的影响

污泥基生物炭内源重金属和养分含量因污泥来源的不同而差异较大。为探索污泥基生物炭“还田”后，其内源重金属变化和养分的去向问题，采用干湿交替对污泥基生物炭模拟老化处理，分析老化前后污泥基生物炭的Cu、Zn金属形态及TCLP浸出毒性的变化；研究污泥基生物炭BC1和BC2（分别以磷酸二氢钾、磷酸二氢钙与污泥混合后热解制备的生物炭）以5%和10%的质量分数与鲜土混合老化后对污泥基生物炭内源重金属稳定性及土壤有机碳和有效磷含量变化的影响。结果表明：两种污泥基生物炭与土壤混合老化后会使土壤中SiO2含量增加，但不会改变土壤的吸附类型；污泥基生物炭的添加会增加土壤的比表面积，其中BC2增幅较大，为36.17 m2/g；施加两种污泥基生物炭土壤中Cu、Zn生物有效性均有不同程度的降低。TCLP浸出毒性量相比老化前降低（BC1约降低37.5%）。此外，BC1对土壤有效磷的提升效果优于BC2（BC1 70 mg/kg，BC2 30 mg/kg）；BC2对土壤有机碳的提升效果优于BC1（BC2 2.2%，BC1 1.15%）。BC2还田更有利于Cu、Zn的固定以及土壤有机碳和有效磷的提升。     

TCLP Heavy Metal Leaching of Personal Computer Components

Electronic waste (E-waste), including all obsolete electronic products, has become the fastest growing component in the solid waste stream. Personal computers (PCs)—the most significant component in E-waste stream—were studied for their potential leaching toxicity of contaminants. All the components in a PC that are composed of, or contain printed wire boards (PWBs) including the motherboard, various expansion cards, disk drives, and power supply unit were tested by the toxicity characteristic leaching procedure (TCLP). The total contents of eight heavy metals including arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver in the PWBs and their TCLP leaching from the PWBs were examined. Among these eight heavy metals lead was found to be the predominant element that causes the toxicity characteristic of the PC components. The lead concentrations in the TCLP extracts of the vast majority of the PWBs ranged from 150 to 500?mg/L, which are 30–100 times the regulatory level of 5?mg/L for classifying a waste as hazardous. The motherboard in a PC contributed 50–80% of the total lead that could leach out from all the PWBs in the PC under the TCLP test conditions. The contents of barium and silver were found to be high in some components, but they were not leachable under the TCLP test conditions. The contents of other five elements in all the PC components were hardly detectable. They would not have the potential to cause toxicity characteristic leaching concern.     

从钴冰镍浸出液中回收镍钴

以Na2S为沉淀剂,采用硫化沉淀法从钴冰镍三段浸出液中回收其中的钴、镍等有价金属。通过单因素试验,考察了Na2S的加入量、酸度(pH)、反应温度和时间等因素对浸出液中铁、镍、钴沉淀率的影响。结果表明,适宜工艺条件为Na2S的过量系数3.0,pH=3.0～3.5,反应温度60℃,反应时间2h,钴、镍、铁的沉淀率分别为99%、98%、90%。     

Two-stage treatment process of pickling wastewater in the cold-rolling production of stainless steel

Based on the characteristics of pickling wastewater in the cold-rolling production of stainless steel,a new processing route,featuring source sludge reduction,wastewater two-stage treatment,heavy metal-contained sludge and calcium salt sludge separating recovery,was proposed.As shown by the research results,after the two-stage process treatment,the effluent water can steadily reach the emission standards,the sludge yield can be decreased by more than 8%;within the heavy metal-contained sludge,the recovery rates of Fe,Cr and Ni can either reach or surpass 95%,and the total content of F and S can drop to around 3%.Therefore,the sludge in the front part can be used as ferric dust.In the calcium salt sludge,the recovery rate of F can either reach or surpass 85%,and the total contents of Fe,Cr and Ni can fall below 0.5%.So the sludge in the rear part can be used as fluorgypsum or fluorite.Meanwhile,the results of the analysis on heavy metals leaching toxicity and morphologic distribution indicate that the two kinds of sectionalized sludge are not classified as hazardous wastes,which have a stable behavior and better utilization values compared with the former mixed-sludge.     

铅冶炼渣的重金属释放行为

以原生铅火法冶炼的烟化水淬渣为研究对象,通过批次浸出试验与动态淋溶试验研究了铅冶炼渣的重金属释放特性,同时考察了浸提剂类型和pH对重金属释放的影响。结果表明,铅冶炼渣属于第Ⅰ类一般工业固体废物,渣中残留的各种重金属在水浸和模拟酸雨浸出条件下的平衡溶出浓度均低于0.1 mg/L。铅冶炼渣中的锑和铅具有较大的淋溶释放量,经过12小时,锑和铅的累积淋溶量分别达到8.3 mg/m2和22 mg/m2。铅冶炼渣的重金属释放行为应同时关注其平衡浸出浓度和动态释放行为。     

磷酸盐沉淀法除铬热力学研究

除铬是含铬电镀污泥湿法冶金过程重要步骤.针对磷酸盐沉淀法从溶液中净化除铬过程进行热力学分析,绘制了25 ℃时Me-P-H₂O(Me: Cr(III), Zn(II), Cu(II), Fe(II), Fe(III), Ni(II))系组浓度对数-pH图,利用热力学平衡图对磷酸盐沉淀法从含铁等金属元素中净化除铁和磷酸铬碱分解过程进行热力学分析.结果表明,pH值为1.0 ~ 5.0磷酸盐形成由易至难依次为Cr(III)>Fe(III) >Fe(II)>Ni(II)>Cu(II)>Zn(II); 磷酸盐沉淀法难以有效地将Cr(III)与Fe(III)分离,而可分离Cr(III)和Fe(II),且较优pH约为2;整个pH值范围Me-P-H₂O系可以分为难溶磷酸盐稳定区、Me(OH)_n稳定区; 高pH区磷酸盐中的Me转变为稳定的Me(OH)_n,实现磷酸盐碱分解.验证实验表明,加入1.1倍理论量的磷酸钠,控制沉淀pH值为2.0,铬、铁、锌、铜、镍沉淀率分别为94.12 %、5.51 %、0.33 %、0.22 %、0.34 %; 氢氧化钠分解磷酸铬时,磷、铬浸出率分别为90.63 %、5.10 %,实现磷铬有效分离.实验与理论基本相符.      

Leaching behavior of metals from a limonitic nickel laterite using a sulfation–roasting–leaching process

The leaching behavior of metals from a limonitic laterite was investigated using a sulfation–roasting–leaching process for the recovery of nickel and cobalt. The ore was mixed with water and concentrated sulfuric acid followed by roasting and finally leaching with water. Various parameters were studied including the amount of acid added, roasting temperature and time, sample particle size, addition of Na₂SO₄ and solid/liquid ratio in leaching process. More than 88% Ni, 93% Co and < 4% Fe are extracted under the determined conditions. Simultaneously, about 90% Mn and Cu, 70% Mg, 45% Al, 25% Zn, 4% Cr and Ca are extracted respectively. The pH of the leach solution is about 2. The leaching efficiency is independent of sample particle size due to decomposition of ferric sulfate formed during roasting. The roasted mass was characterized by various physico-chemical techniques such as DSC/TGA, XRD and SEM. This process provides a simple and effective way for the extraction of nickel and cobalt from laterite ore.     

Assessment of Fossil Fuel Fly Ash Formulations in the Immobilization of Hazardous Wastes

In this work, a simple and inexpensive method is introduced for the immobilization of the hazardous elements Cd, Pb, and Fe from their aqueous solutions in compressed fossil fuel fly ash formulations, as candidates for waste forms. The molded formulations were prepared by initially mixing the hazardous waste solutions with the fossil fuel fly ash material at a constant ratio (17%). Then the resulting pastes were pressed at the appropriate pressure using a manual hydraulic press. The compressed formulations revealed good water resistance, compression strength, and radiation resistance. Leachability investigations of the molded matrices were performed in terms of the accelerated leach test, the toxicity characteristic leaching procedure (TCLP), and long-term leach tests. The TCLP results obtained for Cd and Pb were well below their TCLP limits. On the other hand, the accelerated and long-term leach tests showed a similar behavior. The properties of the compressed formulations revealed their high performance as an alternative for waste forms as indicated by their durability, compression strength, and leachability. The low leachability of Cd, Pb, and Fe from the compressed fly ash formulations could be attributed to a dual mechanism of microencapsulation and/or chemical fixation.     

Leaching Behavior of Lead, Chromium (III), and Zinc in Cement/Metal Oxides Systems

This paper reports the study of the leaching behavior of cement/metal oxides mixtures containing lead, chromium (III) and zinc oxides. A fractional factorial design of experiments (24?1) was carried out considering four factors, the concentration of ZnO, Cr2O3, PbO, and Fe2O3 in the formulations. Iron oxide was also included in the experimental design as it is usually the main constituent of industrial wastes from thermal processes, where lead, chromium and zinc oxides are also found. After 56 days of curing, samples were subjected to the Acid Neutralization Capacity Test and the concentrations of Cr, Zn, and Pb were determined in the leachate at different pH after filtering. The output variables for the analysis of the experimental data were the concentration of metals at initial pH (in water), at pH 9, 7, and 4, and the acid neutralization capacity of the samples at pH 9. The analysis of the results indicates that the immobilization of Zn and Pb in Portland cement is poor; these metals behave as their amphoteric hydroxides. However, the leaching of Cr (III) is in the range found in the control sample, indicating that the stabilization of Cr (III) is successful.     

Pilot Plant Study of Simultaneous Sewage Sludge Digestion and Metal Leaching

This research is related to a preindustrial pilot scale study of the performance of the simultaneous sewage sludge digestion and metal leaching (SSDML) process for decontamination and stabilization of sewage sludge. Ten batch tests were carried out in two 4?m3 bioreactors under various conditions of operation. Results indicated that the addition of 1.0 to 1.5?g?S0/L, which is the equivalent of approximately 30 to 50?kg?S0 per tons dry sludge, is sufficient to obtain conditions of acidity (pH<2.5) and oxido-reduction potential greater than 500 mV necessary for an effective solubilization of toxic metals. The final average of metal solubilization in the output sludge during the SSDML process varied in the following ranges: 25–78% Cd, 9–32% Cr, 48–100% Cu, 77–99% Mn, 15–53% Ni, 12–47% Pb, and 66–100% Zn. The N, P, and K contents were also preserved in the decontaminated sludge. Moreover, the use of low concentrations of elemental sulfur makes it possible to obtain decontaminated sludge with a low total sulfur content (1.4–1.5% S) compatible with agricultural use. The suspended solids removal calculated for the SSDML process was slightly lower, (2.5±0.4)% volatile suspended solids per day, than those reached using standard aerobic digestion. Finally, the SSDML process was found to be effective in removing bad odors and in the destruction (99–100%) of indicator bacteria.     

Ex Situ Electroreclamation of Heavy Metals Contaminated Sludge: Pilot Scale Study

The ex situ remediation of heavy metals-contaminated industrial sludge (pH = 10.35, Zn = 3,500 mg∕kg) by electroreclamation (I = 2.5 A) was studied at pilot scale (42.5 kg of sludge). This research focused on acidification of sludge and electrochemically induced migration of metals, emphasizing their partitioning prior to electroreclamation. The sludge was preacidified to an initial pH of 4.5. After treatment, a very low anode reservoir pH (near 0) was reached, and the average sludge pH was 2. Addition of 1 M HNO3 to the cathode reservoir prevented basic conditions in the sludge. In accordance with selective sequential extraction results, a low migration of Zn and Cu was obtained. In the anode region, Zn and Cu concentrations decreased by 33 and 39%, respectively, and increased in the cathode region by 33 and 26%, respectively. These metals were concentrated in the cathode area but were not effectively transported onto the cathode. Mn appeared to be more mobile than other metals. After 10 days of current application, a layer mainly composed of Ca, Fe, and Mn appeared on the cathode surface.     

Growth stimulation of sulfur oxidizing bacteria for optimization of metal leaching efficiency of fly ash from municipal solid waste incineration

Sulfur oxidizing bacteria were used to leach metals bound in municipal solid waste incineration fly ash. Pure or mixed cultures of Thiobacilli with or without addition of anoxic sewage sludge were incubated with various amounts of fly ash for several weeks. Co-cultures with Thiobacilli and sewage sludge grew faster than pure cultures of T. thiooxidans or cultures with only sewage sludge as inoculum. The addition of sewage sludge increased the rate of growth of sulfur oxidizing bacteria and simultaneously enhanced the acidification of the suspension. As a result, the time for fly ash processing was reduced by 50%. Thiobacilli were able to grow in the presence of up to 8% (w/v) fly ash. Depending on the amounts of fly ash added, the final pH, and the concentration of sulfuric acid formed, different amounts of metals were leached: over 80% for Cd, Cu, and Zn, 60% for Al and approx. 30% for Fe and Ni (totally, approx. 50% of the heavy metals present in the fly ash) were extracted.     

重金属加压浸出技术现状及展望

加压浸出作为一种高效的湿法冶金手段,迄今为止已在铜、锌、镍、钴等重金属行业,以及铀、钼、黄金和铂族等稀贵金属行业得到推广应用。总结了重有色金属铜、铅、锌、镍、钴行业和冶炼过程副产物加压浸出技术研究和工业化应用现状,包括复杂硫化铜矿、铜钴矿、硫化砷渣、黑铜泥、铜阳极泥、白烟尘和铜钴冶炼转炉渣加压浸出,复杂硫化锌矿、锌浸出渣、赤铁矿除铁、镓锗富集物、铜渣等加压浸出,硫化镍矿、红土镍矿、白合金、铜渣和钴冰铜加压浸出等。最后,对加压浸出技术在重有色金属行业未来发展趋势进行了展望。     

某砒霜厂历史遗留砷渣组成分析及浸出特性

对广西某砒霜厂历史遗留砷渣进行组成分析及浸出特性研究。结果表明,供试砷渣为酸性渣,pH为3.36,主要重金属为As、Zn、Pb、Cu、Cd,总量分别为17 404、2 043、1 459、1 376、570 mg/kg。重金属赋存矿物主要为含砷褐铁矾、臭葱石、砷铅铁矿、水砷铁铜石、锌铁尖晶石和铁闪锌矿等。砷渣中需稳定化处理的重金属为As、Zn、Cu、Cd,其硫酸-硝酸法浸出浓度分别为0.69、85.33、41.62、2.58 mg/L,浸出液pH为3.65。砷渣自身具有较强的酸缓冲能力。要实现砷渣As、Zn、Cu、Cd的同步稳定化,需使用强碱性多功能复合稳定化材料。     

二乙三胺五乙酸-三乙醇胺-硝酸钙体系浸取土壤中8种重金属有效态

采用土壤中重金属有效态指标来评价耕地土壤污染状况对反映土壤真实污染状况有重要意义,而在对土壤中重金属有效态进行测定时需先对其进行浸取。在采用二乙三胺五乙酸(DTPA)-三乙醇胺(TEA)-CaCl₂复合浸取剂对土壤中重金属有效态元素浸取时发现有效态Zn的空白较高,对有效态Zn的测定有一定的影响。按DTPA-TEA-CaCl₂复合浸取剂中各组分浓度配制成相应的DTPA、TEA和CaCl₂单组分水溶液,并对其中有效态Zn空白进行测定,结果发现DTPA-TEA-CaCl₂复合浸取剂中有效态Zn空白的93%以上来源于CaCl₂。据此,实验提出采用Ca(NO₃)₂替代DTPA-TEA-CaCl₂体系中的CaCl₂来对土壤中重金属有效态元素进行浸取,即提出了一种浸取土壤中重金属有效态元素的新体系DTPA-TEA-Ca(NO₃)₂,并对其浸取的条件进行了优化。结果表明,采用DTPA-TEA-Ca(NO₃)₂体系浸取的最佳条件为:控制0.005mol/L DTPA-0.1mol/L TEA-0.01mol/L Ca(NO₃)₂溶液的pH值为7.2,土液比(土壤质量(g)与浸取剂体积(mL)之比)为1∶4,于20℃条件下在往复振荡器上以180r/min的速率振荡浸取2h时效果最佳。分别采用DTPA-TEA-Ca(NO₃)₂和DTPA-TEA-CaCl₂两种体系对土壤标准样品中Cu、Pb、Zn、Ni、Cd、Cr、As和Hg共8种重金属有效态进行浸取并对测定后的结果进行对比,结果表明,采用两种方法浸取后,各元素有效态的测定值保持一致,且与认定值相符,这表明采用这两种体系对这8种重金属有效态元素浸取的效果是一样的。试验进一步发现,采用DTPA-TEA-Ca(NO₃)₂体系浸取时,Zn有效态的测定值与其认定值更加接近,且其空白平均值也较DTPA-TEA-CaCl₂体系低约81.4%,这进一步验证了浸取时采用Ca(NO₃)₂替代DTPA-TEA-CaCl₂体系中的CaCl₂可有效降低Zn有效态空白对测试结果的干扰。     

软锰矿协同氧化浸出硫化渣回收锰钴镍工艺研究

以电解二氧化锰过程中硫化除重金属的硫化渣为原料,基于热力学分析结果,以稀硫酸为浸出剂,辅以软锰矿协同氧化浸出硫化渣,以回收其中的锰、钴、镍有价金属。考察了矿渣比、始酸浓度、液固比、反应温度对锰、钴、镍浸出率的影响。结果表明,适宜条件为：温度363.15 K、矿渣比0.08、始酸浓度90 g/L、反应时间180 min,锰、钴、镍的浸出率分别为93.5%、87.4%、86.3%。     

含铅土壤中铅的浸出行为

采用BCR连续浸提法分析含铅土壤中铅的存在形态,通过静态溶浸与动态淋滤试验研究了土壤中铅的浸出行为,结合浸出毒性分析,探讨了添加活性炭对土壤中铅的稳定性影响。结果表明,供试土壤中可交换态铅可转化为可还原态和可氧化态形式存在,活性炭对不稳定态的铅有较强吸附作用。添加活性炭对降低土壤中铅的浸出有一定效果,并且与活性炭性质和淋溶体系pH有关,醋酸体系浸提剂比硫酸体系对铅的浸出浓度影响更大。