Treatment of Cr(VI) in COPR Using Ferrous Sulfate–Sulfuric Acid or Cationic Polysulfides

Column tests were conducted to evaluate two treatment strategies for reducing and stabilizing hexavalent chromium, Cr(VI), in chromium ore processing residue (COPR): permeation with a FeSO4–H2SO4 solution and blending with a cationic polysulfide reagent (CaSX). Cr(VI) leached at concentrations exceeding 50?mg/L from untreated COPR permeated with synthetic groundwater for >20 pore volumes of flow (PVF), and concentrations of Cr(VI) in the solid phase remained high (6,600?mg/kg). Permeation with solutions containing FeSO4–H2SO4 eliminated Cr(VI) from the effluent after initial, elevated leaching of Cr(VI) (100–1,500?mg/kg); however, high solid-phase concentrations of Cr(VI) remained in the column residuals (>1,300?mg/kg). COPR treated with CaSX leached Cr at <0.33?mg/L for 23.5 PVF and had solid-phase concentrations of Cr(VI) <10?mg/kg, although mineralogical analyses of treated solids showed potential chromate-containing mineral phases. Mineralogical analyses showed that precipitation and cementation occurred in the pore space of the COPR permeated with FeSO4–H2SO4, initially lowering the hydraulic conductivity > two orders of magnitude. However, acid dissolution channels eventually formed, resulting in preferential flow. COPR permeated with FeSO4–H2SO4 contained less brownmillerite and Cr(VI)-bearing hydrocalumite and hydrogarnet relative to untreated COPR. For COPR treated with CaSx, S encapsulated the subparticles of COPR with some micropore penetration, suggesting permanence of excess reductant after leaching with 23.5 PVF of synthetic rainwater.     

碳酸钠溶液堆浸-硫酸亚铁还原联合解毒铬渣

以碳酸钠溶液作浸出剂、硫酸亚铁作还原剂,对循环碳酸钠溶液堆浸—硫酸亚铁还原联合解毒铬渣新工艺进行研究。结果表明,在整个解毒过程中,浸出液pH在10～12变化,浸出液经还原后溶液中Cr(VI)的实际浓度略高于其理论值;第一次浸出后,铬渣中钙铁石或水榴石中的Cr(VI)被大量浸出,浸出液中碳酸钠浓度由浸出前的9.3g/L下降至7.98g/L,Cr(VI)浸出率为62.67%;在此后的循环解毒过程中,浸出液中碳酸钠浓度均维持在8g/L左右,Cr(VI)浸出率增加缓慢;循环处理12次后,铬渣中Cr(VI)浸出率达85%,最终解毒渣中残留Cr(VI)主要存在于水滑石中;铬渣粒度显著影响其解毒效果,当粒度小于0.15mm时,最终解毒渣的毒性浸出液中Cr(VI)和总Cr浓度分别为1.98mg/L和2.45mg/L,达到一般工业固体废物填埋的标准。     

Identification of an accurate soil suspension/dispersion modeling method for use in estimating health-based soil cleanup levels of hexavalent chromium in chromite ore processing residues

The primary health concern associated with chromite ore processing residues (COPR) at sites in Hudson County, NJ, is the inhalation of Cr(VI) suspended from surface soils. Since health-based soil standards for Cr(VI) will be derived using the inhalation pathway, soil suspension modeling will be necessary to estimate site-specific, health-based soil cleanup levels (HBSCLs). The purpose of this study was to identify the most appropriate particulate emission and air dispersion models for estimating soil suspension at these sites based on their theoretical underpinnings, scientific acceptability, and past performance. The identified modeling approach, the AP-42 particulate emission model and the fugitive dust model (FDM), was used to calculate concentrations of airborne Cr(VI) and TSP at two COPR sites. These estimated concentrations were then compared to concentrations measured at each site. The TSP concentrations calculated using the AP-42/FDM soil suspension modeling approach were all within a factor of 3 of the measured concentrations. The majority of the estimated air concentrations were greater than the measured, indicating that the AP-42/FDM approach tends to overestimate on-site concentrations. The site-specific Cr(VI) HBSCLs for these two sites calculated using this conservative soil suspension modeling approach ranged from 190 to 420 mg/kg.     

In situ reduction of hexavalent chromium in alkaline soils enriched with chromite ore processing residue

In investigating chromium sites in New Jersey, it has been observed that an organic-rich 0.5- to 4-foot-thick layer of decayed vegetation (locally known as "meadowmat") underlying the chromium-containing material acts as a natural barrier to the migration of Cr(VI). The groundwater in a sand layer directly beneath the meadowmat has been shown to contain low or nondetectable levels of chromium. The meadowmat is under highly reduced conditions due to bacterial activity associated with the organic material. Based on the observed ability of the meadowmat to reduce Cr(VI) to Cr(III), the feasibility of in situ reduction of Cr(VI) to Cr(III) at chromite ore processing residue (COPR) sites was investigated in biologically-active, laboratory-scale test columns. COPR typically has a high pH (in excess of 12) and may contain total chromium concentrations as high as 70,000 mg/kg. Experimental results demonstrated that the addition of a mineral acid (to lower the pH to between 7.0 and 9.5) and a bacteria-rich organic substrate (fresh manure) resulted in the reduction of Cr(VI) to the less toxic and less mobile trivalent form. Pore water Cr(VI) was reduced from approximately 800 mg/L to less than 0.05 mg/L over a period of eight months. This is less than the U.S. Environmental Protection Agency's (EPA) Maximum Contaminant Level (MCL) for chromium in drinking water of 0.1 mg/L. Solid phase Cr(VI) concentrations decreased from approximately 2,000 mg/kg to less than 10 mg/kg in the columns over a period of 11 months while the total chromium concentrations remained unchanged. Toxicity Characteristic Leaching Procedure (TCLP) extract from the treated columns met the regulatory limit of 5 mg/L of Cr, whereas the untreated samples had TCLP extract concentrations greater than 40 mg/L. This study demonstrated the potential applicability of in situ reduction to soils contaminated with Cr(VI) by adjusting the pH to between 7.0 and 9.5 and mixing in a bacteria-rich organic substrate.     

In Situ Source Treatment of Cr(VI) Using a Fe(II)-Based Reductant Blend: Long-Term Monitoring and Evaluation

The long-term effectiveness of an FeSO4+Na2S2O4 reductant solution blend for in situ saturated zone treatment of dissolved and solid phase Cr(VI) in a high pH chromite ore processing solid waste fill material was investigated. Two field pilot injection studies were conducted that showed sustained treatment of Cr(VI) over evaluation periods of more than 1,000 days. No well or aquifer formation clogging was observed during injection although treatment was limited to the pore volume displacement radius of the injected reductant. Analysis of posttreatment core samples suggested >85% treatment effectiveness of solid phase Cr(VI), whereas lab tests suggested treatment of the solid phase Cr(VI) can be complete provided the chromite ore processing solid waste sediments are sufficiently dosed with the reductant. The sustained treatment of dissolved phase Cr(VI) migrating through the treatment zones for more than 1,000 days following injection provided strong evidence of a residual treatment capacity having been imparted to the formation solids. Scanning electron microscopy–energy dispersive x-ray spectroscopy analyses of posttreatment core samples indicated that much of the Cr(VI) may be removed through the formation of a Cr-bearing precipitate, possibly a complex carbonate, characterized by an Fe:Cr molar ratio of roughly 1:1.     

Contaminant Leaching from Stabilized/Solidified Acid Tars

This work investigates the leachability-related properties of acid tars treated with portland cement (CEM I), with the addition of high carbon fly ash (HCFA), as a novel binder for the immobilization of hydrocarbons. The leachate pH, acid neutralization capacity (ANC), and leaching of metals and sulfates from the treated acid tars were investigated. The effect of acid tar type, CEM I:HCFA ratio, and curing time on hydrocarbon leaching was also studied using factorial design experiment. ANC results show that acid tars had detrimental effect on the formation of cement hydration products. The overall results indicate that metal was not released in high concentration from the stabilized/solidified acid tars; hence their leaching is not of great environmental concern. The amount of leached sulfates was significantly lower than untreated acid tars and was attributed to ettringite formation. Factorial analyses show that all studied factors significantly affected hydrocarbon leaching. HCFA addition resulted in reduction in hydrocarbon leaching but led to an increase in sulfate leaching. This work shows that HCFA improved the immobilization of hydrocarbons and may represent an inexpensive binder for stabilization/solidification of wastes containing organic contaminants.     

铬渣无害化综合利用的实践

本文根据国内铬渣无害化处理及综合利用的成熟工艺,针对某化工企业遗留的2.3万t铬渣,杂质含量高且成分复杂的特点,采用多种方法结合的思路,较为经济的解决了遗留渣的处理处置问题。并为该企业今后的新渣治理提供了可行方法。对周边环境的保护意义重大。     

Mineralogical and Physical–Chemical Characterization of a Bauxite Ore from Lages,Santa Catarina,Brazil, for Refractory Production

Bauxite is widely used for refractory production owing to its high alumina content and high melting point. Brazil is one of the world's biggest producers of bauxite for refractory applications, and Santa Catarina State can be highlighted as one of the biggest reservoirs of bauxite ore. In spite of this fact, its chemical and mineralogical characteristics are not well known as well as its high temperature properties. The studied ore was completely characterized [chemical (X-ray fluroscence), thermal (differential thermal analysis), mineralogical (X-ray diffraction), and microscopic (optical microscopy and scanning electron microscopy) analyses] and the results showed that the bauxite ore is suitable to be used as a raw material for refractory applications.     

含铬特殊钢渣中总铬及六价铬浸出特性及影响

 含铬特殊钢渣中六价铬具有强氧化性和高毒性,研究不同条件下渣中总铬及六价铬的浸出行为及特征并进行环境风险评估,对后续无害化及资源化利用具有重要的意义。浸出试验结果表明,渣中总铬和六价铬的浸出量随粒度和浸出时间增加而提高,随液固比(即浸提剂溶液体积与待测固体试样质量的比值)增加而降低;六价铬浸出量随体系pH值升高而增加,当pH=11时六价铬浸出量达到最高值2.92 mg/L;总铬浸出量随pH值升高呈现先降低后增加的趋势,当pH=7时,总铬达到最小浸出量2.49 mg/L。经标准浸出程序测定,钢渣中铬及六价铬浸出量分别为4.71和3.36 mg/L,符合固废堆存限值(GB 5085.3—2007),堆存风险较小,但高于行业利用限值(HJ/T 301—2007),需对其进行无害化处理后再进行后续资源化利用。     

贫铬矿生产高碳铬铁的研究

用国内新疆、青海、甘肃等省生产的贫铬矿和越南贫铬矿,配以印度铬矿粉、入炉料控制Cr2O341%～43%,Cr/Fe2.5左右,在6.3 MVA矿热炉中生产符合GB5683-87中高碳铬铁成分的铬铁,效益明显,工艺可行.     

铬渣的微生物治理新技术研究

本研究采用课题组发现的还原Cr（VI）的专属无色杆菌属Ch-1菌株,对铬渣进行微生物治理。结果表明：铬渣渗滤液经该菌处理后,其中的Cr（VI）可达排放标准,沉淀物中Cr（OH）3含量达32.8％,具有实际回收价值。将铬渣进行微生物柱浸,7d后溶液中检测不出cr（VI）;解毒后铬渣中Cr（VI）达到国家危险废物毒性鉴别标准（GB5085-1996）。     

Cr(VI) Removal from Water with Amorphous Graphite Concentrate Contaminated by Iron

This work attempted to explore the feasibility of using iron-contaminated graphite concentrate as an effective adsorbent for Cr(VI) removal from polluted water. Adsorption isotherm and kinetics were conducted to investigate the Cr(VI) removal capacity by the iron-contaminated amorphous graphite concentrates. In addition, SEM-EDS, XPS were carried out to further examine the solid samples. The results showed that amorphous graphite concentrate had a 1.52 mg/g adsorption capacity of Cr(VI), with the adsorption being fitted well with the pseudo-second-order kinetics model. In addition, chemical adsorption of Cr(V) on iron-contaminated graphite concentrate due to the formation of ≡Fe-O₄HCr and Fe₂-(CrO₄)₃ complexes was proposed. This study revealed that iron-contaminated amorphous graphite concentrate would be a cheap and good adsorbent for the removal of Cr(VI) from contaminated water.     

硫脲法从低品位含金硫化矿及其焙砂酸浸渣中回收金

本工作采用硫脲法从钴铜硫化矿及其经硫酸化焙烧,酸浸钴铜后的渣中对低品位金进行了浸取研究.直接浸取硫化矿,金的溶出率低,操作参数如电位、pH值等不稳定,试剂耗量大;而从酸浸渣中浸取金的溶出率高,可达91.0%以上,数据重现性好,试剂消耗大大降低,操作稳定.优化了浸取条件,从而降低了硫脲消耗,耗量是1.78kg/t矿.最后,用还原铁粉和活性炭从硫脲浸取富液中回收金进行了探索,效果良好.试验结果表明,硫脲法具有潜在的工业性应用推广价值.     

Selective adsorption of chromium(VI) from zinc(II) and other metal ions using persimmon waste gel

An adsorption gel was prepared from persimmon waste, a cellulosic material, rich in polyphenolic compounds, which exhibits a high affinity for chromium(VI). It was prepared by cross-linking persimmon waste with concentrated sulphuric acid. Adsorption tests for different metal ions such as Cr(VI), Cr(III), Fe(III), Zn(II), Cd(II) and Pb(II) from aqueous solution at pH values ranging from (pH 1 to 5) found Cr(VI) to be selectively adsorbed on the cross-linked gel over the other metal ions studied. The adsorption isotherm of Cr(VI) followed the Langmuir type of adsorption and exhibited a maximum loading capacity of 7.18 mol kg^− 1 at pH 1. Selective removal of Cr(VI) from Zn(II) was successfully demonstrated by using a column packed with the persimmon waste gel.     

Recovery Problems in Gold Ore Processing with Emphasis on Heap Leaching

The present paper briefly describes the methods of gold ore processing and the associated problems are grouped into mineralogical, chemical and physical. The processing of low grade gold ores by heap leaching is an important technological development. But a major drawback in heap leaching process is low recovery of the precious metals. The problems that generally lead to a low gold recovery and the possible solutions are discussed.     

鲕状赤铁矿特征及选冶技术进展

论述了鄂西高磷鲕状赤铁矿的资源状况、矿物组成、矿石结构、矿物工艺学特征,对处理、利用该类矿石存在的问题进行了分析,介绍了常用反浮选、强磁选、磁化焙烧-弱磁选、直接还原焙烧、酸浸及微生物浸出等选冶技术的现状,展望了高磷鲕状赤铁矿还原-磁选、磁选-絮凝脱泥-反浮选等选矿联合流程的发展趋势。     

Predicting the rates of recovery from selective chemical reaction of ores — A specific example: Leaching of chalcopyrite in acid with oxygen

Correlations previously reported (Roach and Prosser, 1975) have been used to calculate the rate of recovery of copper from lumps of porphyry ore by selective leaching of chalcopyrite. The mineralogical data used were independently determined; kinetic data obtained from the ore were not required in the calculations. The predicted rate curves are within a factor of 2x those determined experimentally by Braun et al. (1974), which is satisfactory for preliminary process design. Substantially less time was required to obtain the information compared with conventional testwork.     

仙人岩地表金矿石氰化浸出试验

根据仙人岩地表金矿石的特性,比较了三种氰化方法的优劣,并考察矿石预处理、矿石粒径、鼓风搅拌和焙烧对金浸出率的影响。结果表明,仙人岩地表低品位金矿石采用堆浸法的成本低、处理量大、更为合理。     

Bioreduction of Hexavalent Chromium in Flow-Through Quartz Sand Columns

Hexavalent chromium (Cr(VI)) contamination of soil and groundwater is a major environmental concern for some industrial sites and most of the U.S. Department of Energy sites. Cr(VI) is toxic and fairly mobile in groundwater. Bioreduction of Cr(VI) to less toxic and less mobile Cr(III) is considered to be a feasible option. Among the Cr(VI) reducing bacteria, Shewanella oneidensis MR-1 (MR-1) has been shown to be effective in metal reduction under anaerobic conditions. Data on bioreduction of Cr(VI) by MR-1 in a flow-through soil column that better approximates the subsurface condition are not available. The objective of this research project was to study the bioreduction of Cr(VI) by MR-1 in a continuous-flow quartz sand column system. MR-1 was found to be very effective in reducing Cr(VI) to Cr(III) for concentrations ranging from 0.055 mM (2.85?mg/L) to 0.006 mM (0.31?mg/L). The amount of Cr(VI) reduced prior to its breakthrough was found to be inversely proportional to its concentration in the feed due to increased inhibition of microbial activity and a residual reduction of 20–45% of Cr(VI) was observed even after its breakthrough.     

Lattice Boltzmann model for simulation on leaching process of weathered elution-deposited rare earth ore

The lattice Boltzmann model with coupled chemical reaction was proposed to simulate the ion exchange process of rare earth leaching and verified by comparison with both empirical correlation of mass transfer coefficient and unreacted-core shrinking model. By simulation, the zonation phenomenon of leaching reagent in the leaching column was presented, and the breakthrough curve of leaching reagent was obtained. When t=50 s, there existed the saturated and exchange zones, and the leaching reagent concentration decreased gradually from 20 to 9.3 g/L. In accordance with the breakthrough curve, the breakthrough capacity of ion-type rare earth ore and the adsorbed ion concentration of leaching reagent were derived, the time of t=25 s was the breakthrough point of ammonium ion in leaching reagent and the breakthrough capacity of the rare earth ore was 125 g/L. Besides, the chemical kinetics parameters used for the solute transfer process of rare earth leaching were obtained by the simulation and then were used to determine the rate-limiting steps of rare earth leaching process.