Molybdenum and Chromium Depletion at Grain Boundary Precipitates Alloy 926

Alloy 926 is a molybdenum-bearing stainless steel and is used in various industrial fields. This material is used as a cladding material for high diameter pipes in oil and gas industry. One opportunity of production of this material is a thermo-mechanical rolling process. Recent studies have shown that an end rolling temperature of 950 °C with subsequent water cooling has comparable corrosion properties with a solution annealed material. The impact of two different quenching and tempering processes on corrosion properties is presented. The microstructure was evaluated with high resolution SEM, and grain boundary precipitates as well as depletion zones were characterized with TEM-EDX line-scans. Isothermal annealing at 760 °C results in formation of Molybdenum rich, Chromium depleted phases. Their microstructure was not clearly detected by electron diffraction, presumably Laves phase is formed. At 900 °C and long term annealing, two s phases are present. One has a similar composition to the above mentioned Laves phase, the other is Molybdenum enriched and Chromium enriched. Thermo mechanically processed materials contains c phases with similar composition. Depletion zones of these phases are quantitatively characterized with respect to width and chemical composition and their impact on corrosion properties is discussed by use of PREN concept.     

烧结温度对钡渣陶瓷砖结构和力学性能的影响

以钡渣和高岭土为原料,采用固相烧结法制备钡渣陶瓷砖,通过抗压强度、吸水率及X射线衍射仪(XRD)分析,研究了烧结温度对钡渣陶瓷结构和力学性能的影响。研究表明,随着烧结温度升高,钡长石相逐渐增多,晶粒尺寸增大,晶格应变减小,吸水率降低。此外,1100℃烧结的陶瓷具有最佳力学性能,此温度下十二烷基硫酸钠(SDS)添加量为0.8%的陶瓷样品与不含SDS样品相比相结构组成相似,但SDS添加量为0.8%样品抗压强度和吸水率表现更优。因此,合适的烧结温度与SDS添加量都对陶瓷材料的相结构组成、晶粒尺寸、晶格应变、抗压强度和吸水率有重要影响。     

烧结温度对河津赤泥物相和物理性能的影响

为了给赤泥的陶瓷化应用提供基础依据,以山西河津某铝厂赤泥为对象,研究了烧结温度对赤泥物相和物理性能的影响。结果表明：试验用赤泥的主要矿物相为钙铝黄长石和石英,有少量钠长石、钙钛榴石和钙铁榴石。在高于1 000 ℃的温度下烧结时,随着烧结温度的提高,赤泥中石英、钠长石和钙钛榴石的含量逐渐减少,钙铝黄长石和钙铁榴石含量逐渐增加。试验赤泥陶瓷化的适宜烧结温度为1 150 ℃,此时烧结赤泥的体积密度为1.82 g/cm³,吸水率为19.9%,气孔率为36.0%,抗压强度为58.8 MPa。高温下赤泥中钙铝黄长石和钙铁榴石含量的增加及玻璃液相的生成是提高烧结赤泥抗压强度,促进赤泥陶瓷化的关键因素。     

赤泥基陶粒的制备及性能研究

以拜耳赤泥为主要原料,糖蜜酒精废液、玻璃、蔗渣为辅料,制备赤泥基陶粒,采用硬度和显气孔率为主要性能指标,考察各制备因素对陶粒性能的影响,并通过XRD、SEM对陶粒进行表征分析。通过试验得到陶粒的制备工艺:制备原料组配为10 g赤泥、0.7 g Al Cl3、3 g玻璃粉末、0.25 g蔗渣、3.5 g糖蜜酒精废液,焙烧温度950℃,焙烧时间3 h。所制备的陶粒平均硬度为152.8 N,显气孔率为43.04%,磨损率为1.58%。表征分析显示:陶粒中赤泥原有八面沸石组分基本消失;陶粒中出现了非晶态的玻璃相组分;陶粒孔洞丰富,部分内、外孔洞连通。     

Effect of Aqua Blasting,Sandblasting and Laser Engraving on the Corrosion Resistance of Type 316 Stainless Steel

The goal of this paper is to advance our understanding about the influence of commercial surface finishing treatments on microstructure development and corrosion resistance of a type 316L stainless steel. Aqua blasting, sandblasting, and application of a laser barcode engraving treatment were investigated using Focus Ion Beam, X-ray phase analysis, X-ray residual stress measurements, and surface roughness measurements. All surface microstructures were then assessed with atmospheric corrosion tests at 50?°C and 30?% relative humidity. Aqua blasting resulted in compressive surface residual stresses of ??500 to ??600 MPa, with no evidence of strain-induced martensite. Sandblasting led to compressive surface residual stresses of ??700 MPa, also with no evidence of strain-induced martensite. The samples subjected to laser engraving exhibited a recrystallized near-surface microstructure, with tensile surface residual stresses in the order of?+?500 MPa.     

煤矸石制备堇青石质多孔玻璃陶瓷的研究

煤矸石主要由黏土质矿物组成,利用其矿物成分特点可用作制备陶瓷的原料。以煤矸石为主要原料,辅加少量工业氧化铝和氧化镁,制备出堇青石玻璃陶瓷。用X射线衍射物相分析方法研究了陶瓷的物相组成,采用扫描电镜和电子探针研究了陶瓷的显微结构。样品由晶相、玻璃相和气孔组成,晶相主要为堇青石,还有少量莫来石等。堇青石晶体结构中固溶了少量的二价铁,形成了铁堇青石。陶瓷最佳合成温度为1210~1240℃,气孔均为封闭气孔,样品的吸水率接近于0,抗折强度为60 MPa。     

Year-Round Performance of a Passive Sulfate-Reducing Bioreactor that Uses Rice Bran as an Organic Carbon Source to Treat Acid Mine Drainage

The development of compact and cost-effective passive treatment systems is of critical importance for acid mine drainage (AMD) remediation in Japan. The purpose of this study was to construct an AMD treatment system comprising a sulfate-reducing bioreactor using rice bran as a carbon source for sulfate-reducing bacteria (SRB) and to demonstrate its stable operation for at least a year in terms of continuous sulfate reduction and metal removal. Our 35 L bioreactor comprised a packed inoculum layer of a mixture of rice husks, limestone, and field soil, which was covered with rice bran. During operation, the AMD input flow rate was adjusted to 11.7 mL/min (hydraulic retention time, HRT; 50 h). Throughout the year, physicochemical analyses of system input and output AMD samples revealed that both pH and oxidation–reduction potential values were consistent with the process of sulfate reduction by SRB, although this reduction was observed to be stronger in summer than in winter. Efficient metal removal was observed, with concentrations at the outlet port of <0.33 mg/L Zn, <0.08 mg/L Cu, and <0.005 mg/L Cd, more than meeting Japan’s national effluent standards. Illumina sequencing of 16S rRNA genes revealed that Desulfatirhabdium butyrativorans-related species, which belong to a lineage within Deltaproteobacteria, were dominant (39–48% of the total SRB population) within the bioreactor.     

Removal of Metals and Acidity from Acid Mine Drainage Using Municipal Wastewater and Activated Sludge

Co-treatment of acid mine drainage (AMD) and municipal wastewater (MWW) using the activated sludge process is an innovative approach to AMD remediation that utilizes the alkalinity of MWW and the adsorptive properties of the wastewater particulates and activated sludge biomass to buffer acidity and remove metals. The capacity of these materials to treat AMD was investigated in batch mode metal removal tests using high-strength synthetic AMD (pH 2.8, Al 120–200 mg/L, Cu 18–30 mg/L, Fe 324–540 mg/L, Mn 18–30 mg/L, and Zn 36–60 mg/L). Using material from a range of MWW treatment plants, the performance of screened and settled MWW, activated sludges with mixed liquor suspended solids (MLSS) concentrations of 2.0 and 4.0 g/L, and return activated sludges with 6.0 and 7.4 g/L MLSS were compared. Similar trends were observed for the MWW and activated sludges, with removal efficiency generally decreasing in the order Al = Cu > Mn > Zn > Fe. Trends in Fe removal using settled MWW and activated sludges were highly variable, with removal <30 %. Using activated sludges, average removal efficiencies for Al, Cu, Mn, and Zn were 10–65 %, 20–60 %, 10–25 %, and 0–20 %, respectively. Sludge solids concentration was an important controlling factor in metal removal, with removal of Al, Cu, Mn, and Zn increasing significantly with solids concentration. Municipal wastewaters had greater neutralization capacities than activated sludges at high AMD loading ratios. Mixing AMD with screened MWW gave the highest removal efficiency for all metals, achieving average removal of 90–100 % for Al, Cu, and Fe, 65–100 % for Zn, and 60–75 % for Mn. These empirical findings are useful for developing process design parameters in co-treatment systems. Utilizing MWW and activated sludge to remediate AMD can potentially reduce materials and energy requirements and associated costs.     

Tailings Weathering and Arsenic Mobility at the Abandoned Zgounder Silver Mine,Morocco

The abandoned Zgounder Mine (Morocco) was exploited for Ag from 1982 to 1990 and generated nearly 490,000 t of mill tailings before it was closed without being reclaimed. The tailings contain low concentrations of sulfide (mainly as pyrite, sphalerite, and galena) and carbonates (mainly dolomite). Silicates (muscovite, albite, chlorite, labradorite, actinolite, and orthoclase) occur in high concentrations. The most abundant trace elements are As, Ti, Fe, Mn, Zn, and Pb. We studied the geochemical behavior of the mine wastes to identify the main factors controlling drainage water chemistry. Particular emphasis was put on sorption phenomena to explain the low As concentrations in the leachates despite significant As levels in the tailings. Weathering cell tests carried out on various tailings produced two types of contaminated drainage: acidic and neutral. The kinetic test leachates contained high concentrations of some contaminants, including As (0.8 mg L^?1), Co (11 mg L^?1), Cu (34 mg L^?1), Fe (70 mg L^?1), Mn (126 mg L^?1), and Zn (314 mg L^?1). Acidity and contaminants in the leachates were controlled by dissolution of soluble salts and Fe hydrolysis rather than sulfide oxidation. Batch sorption tests quantified the significance of As sorption, and sequential extraction showed that most of the As sorption was associated with the reducible fractions (Fe and Mn oxides and oxyhydroxides).     

纳米镍粉/超细陶瓷涂层的晶化行为研究

采用SEM、XRD等技术对高温下含纳米镍粉的陶瓷涂层材料的晶化行为进行了研究。结果表明, 陶瓷涂层/合金试样在900 ℃下进行真空扩散退火后, 涂层材料发生了晶化现象, 云母作为主晶相在涂层中析出, 纳米镍粉的添加促进了云母晶体的析出。     

Mo 添加量对纳米改性金属陶瓷显微组织的影响

研究了Mo 添加量对铣削用TiC-TiN(nm)-WC-Mo₂C-Ni-Co 金属陶瓷的组织特征、力学性能和断口形貌的影响。结果表明,金属陶瓷的组织为典型的两相结构特征, 其中陶瓷相的芯/壳结构(core/rim structure)与溶解析出机制有关。少量Mo的加入能提高材料的力学性能。断口SEM 分析表明:断裂机理为典型的混合型断裂(穿晶断裂和沿晶断裂), 金属相存在着明显撕裂的痕迹。     

Characteristics and Seasonal Variation of Sediments in Lake Junttiselkä, Pyhäsalmi,Finland

Lake Junttiselkä, located in central Finland, has been loaded by effluents from Pyhäsalmi Zn–Cu mine since 1962 and also receives Pyhäsalmi municipal effluent. A total of 32 top sediment samples (0–2, 2–4, and 4–6 cm) were collected in October 2005 and March 2006 to examine the seasonal variation in sediment composition. Furthermore, two sediment cores of 1 m were taken from the northern and southern parts of the lake (Junttiselkä_N, Junttiselkä_S) to investigate the sedimentation history. Electrical conductivity (EC) was measured from the sediment in situ, and sediment pH, redox values, and EC were measured in the winter from the top samples. The sediment samples were freeze-dried and multi-element determinations were performed using ICP-MS on nitric acid extracts (EPA 3051, acid soluble fraction, AF) and on ammonium acetate extracts (bioavailable fraction, BF). The composition of crystalline and semi-crystalline fractions (CF) was calculated by the formula C_CF = C_AF – C_BF. Due to the high clay content of till in the catchment area, the Al, K, and Mg concentrations in the natural lake sediments (>49 cm) are greater than the average level in lake sediments of Finland (AF). Soil cultivation has increased the sedimentation of fines, which has further increased Al, K, and Mg concentrations in the lake sediments (49–19 cm). Mine effluents have had the greatest impact on sediment concentrations of Cu and Zn, with the recorded levels of 166 mg/kg and 434 mg/kg (<19 cm), respectively, being nine- and threefold greater than the natural concentration level. Also, Ca and S concentrations are elevated. The electric conductivity of pore water was elevated at a depth of 1 m. Seasonal variation in the composition of Junttiselkä top sediments is linked to the oxic/anoxic conditions in the water column during the autumn to winter period. The greatest variation was recorded in the 0–2 cm layer in Junttiselkä_S, where Ca_BF and S_BF concentrations were three and sixfold higher in the winter than in the autumn. Mg_BF, Pb_BF, Sr_BF, Cr_BF, P_BF, U_AF, and Se_AF concentrations also increased in the winter, but Mn_BF, Cu_BF, Cd_BF, Co_BF, Zn_BF, Ba_BF, Ni_BF, Fe_BF, and Al_BF decreased. The seasonal variation in composition was less for CF than for BF, and was also partially different. The most significant difference was an increase in Ca_CF and S_CF concentrations in the winter in Junttiselkä_S, with the reverse situation being observed in Junttiselkä_N. Furthermore, the Fe_CF concentration increased in Junttiselkä_N. Equimolar variations in Ca and S suggest that the precipitation and dissolution of gypsum is the most notable seasonal process in the top sediment layer. The seasonally precipitated S corresponds to only 1.4% of the total load of S from the mine effluents.     

Geochemical Behavior of Mine Tailings and Waste Rock at the Abandoned Cu–Mo–W Azegour Mine (Occidental High Atlas, Morocco)

The abandoned Azegour mine is located in the High Atlas Mountains of Marrakesh (Morocco), and was mined for Cu, Mo, and W. About 850,000 t of waste rocks and tailings were deposited on the surface and have been exposed to weathering for 40 years. The remaining acid-producing potential (AP), acid-neutralizing potential, and geochemical behavior of the Azegour Cu-and Mo-rich tailings were investigated. The tailings were found to contain 9.6–19 wt% sulfur, mostly as sulfate (gypsum, anhydrite, and jarosite) while the waste rocks contain less (1.25–6.58 wt%) sulfur. The waste rocks and tailings contain 0.21–9.24 wt% Mo and 0.003–2.78 wt% Cu. The gangue is mostly composed of quartz, talc, chlorite, pyrophyllite, actonolite, clinoptilolite, and alusite. Lead, zinc, cobalt, arsenic, titanium, and nickel are also present. The calcium, which is mainly expressed as calcite, gypsum, scheelite, and powellite, is present at higher concentrations in the waste rocks (18–22 wt% Ca) than in the tailings (4.7–8.6 wt% Ca). Static ABA determinations showed that the Azegour mine wastes still have high AP, 38–205 kg CaCO₃/t in the waste rocks and 46–387.7 kg CaCO₃/t in the tailings. This was confirmed in weathering cell tests, where the Azegour tailings leachate had a pH range of 1.98–3.19 and high concentrations of SO₄ (468–45,400 mg/L), Ca (230–675 mg/L), Fe (3–55,900 mg/L), Mn (0.1–1,430 mg/L), and Cu (2.3–9,000 mg/L). The Mo concentrations were high (35 mg/L) during the two first weeks of kinetics tests; W concentrations were below the 0.005 mg/L detection limit.     

Trace Element Scavenging in Dry Wash Surficial Sediments in an Arid Region of Southern Nevada,USA

Sediment samples were collected from a dry wash in Nelson, Nevada where the Techatticup Mine and Mill operated between 1850 and 1960. Samples were used to evaluate movement and behavior of certain metals and metalloids including aluminum, arsenic, barium, cadmium, copper, iron, manganese, lead, and vanadium. The data show that some metals and metalloids are more concentrated on larger particles whereas others show the opposite tendency. For example, As was greatest on silt fractions and least on coarse fractions, while Se was detected only on silts. Chromium, Cu, Fe, Mn, Pb, and Zn concentrations all increased with decreasing particle size (silt > sand > coarse), whereas Al, Ba, and V showed the opposite trend (silt < sands < coarse).     

Upper and Lower Concentration Thresholds for Bulk Organic Substrates in Bioremediation of Acid Mine Drainage

Acidic pit lakes can form in open cut mine voids that extend below the groundwater table. The aim of this research was to determine what bulk organic material concentrations best stimulated sulphate-reducing bacteria (SRB) for acid mine drainage (AMD) treatment within a pit lake. An experiment was carried out to assess the effect of different substrate concentrations of sewage sludge on AMD bioremediation efficiency. Experimental microcosms were made of 300 mm long and 100 mm wide acrylic cores, with a total volume of 1.8 L. Four different concentrations of sewage sludge (ranging from 30 to 120 g/L) were tested. As the sewage sludge concentration increased, the bioremediation efficiency also increased, reflecting the higher organic carbon concentrations. Sewage sludge contributed alkaline materials that directly neutralised the AMD in proportion to the quantity added and therefore played a primary role in stimulating SRB bioremediation. The lowest concentration of sewage sludge (30 g/L) tested proved to be inadequate for effective SRB bioremediation. However, there were no measurable beneficial effects on SRB bioremediation efficiency when sewage sludge was added at concentrations >60 g/L. We compared our results with existing literature data to develop a conceptual model for remediation of AMD in pit lakes through organic material amendments. The model indicated that labile organic carbon availability was more important to the bioremediation rate than AMD strength, so long as iron and sulphate concentrations were not limiting. The conceptual model also indicates that bioremediation may still occur when only low concentrations of organic carbon are present in the pit lakes, albeit at a very slow rate. The model also demonstrates the presence of an organic material amendment threshold where excess organic carbon does not measurably influence the final outcome. The conceptual model defined is well supported by the results of the microcosm experiment.     

Biodegradation of Biosolids Under Aerobic Conditions: Implications for Cover Materials for Sulfide Mine Tailings Remediation

Sewage sludge residue (biosolids) was investigated for its potential as a long-term tailings cover. Biosolids may prevent oxygen diffusion into underlying sulfide tailings through microbial aerobic biodegradation of organic matter. Biosolids were investigated at laboratory-, pilot-, and field-scale using analysis of total organic matter (TOM) mass reduction and O₂, CO₂, CH₄ concentrations to quantify the biodegradation rate. A 156-day, open microcosm experiment, in which the loss of biosolids mass over time at differing temperatures, mimicking ambient (20–22 °C), mesophilic (34 °C), and thermophilic (50 °C) conditions, indicated that TOM biodegradation was best in the mesophilic temperature range, with 14.8, 27.2, and 26.7 % mass depletion at ambient, mesophilic, and thermophilic conditions, respectively. The data was correlated to field-scale data that evaluated biodegradation rates via decreasing O₂ and increasing CO₂ concentrations. Field biodegradation rates were less than laboratory rates because lower mean annual temperatures (0.6–0.7 °C) diminished microbial activity. A calibrated model indicates that 20 % of a field application of biosolids will degrade within 2 years. However, the rate declines with time due to exhaustion of the most readily degradable organic fraction. If biodegradation cannot be maintained, the long-term effectiveness of biosolids as a covering material for mine tailings remains a concern.     

Geochemical Modelling of the Effects of a Proposed Uranium Tailings Pond on Groundwater Quality

The impact of a proposed uranium tailings pond on groundwater quality was assessed by geochemical modelling. Groundwater samples were collected from six dug wells in the Nalgonda district, Andhra Pradesh, in southern India, once every 2 months from March 2008 to January 2010, and analysed for calcium, magnesium, sodium, potassium, chloride, sulphate, carbonate, bicarbonate, and uranium. Prediction of groundwater quality was carried out for 100 years using PHREEQC to assess the effects of infiltration of water from the proposed tailings pond. The sensitivity of the model for variations in porosity, hydraulic gradient, hydraulic conductivity, and concentration of uranium in the tailings was evaluated. Geochemical modelling predicts that if the chemical composition of the tailings water is maintained at about the expected mean concentrations, and an appropriate liner is installed with an infiltration rate ≤1.0 × 10^?9 m/s, the concentration of solutes in the groundwater will be increased from present background levels for a down-gradient distance of up to 500 m for the anticipated life of the mine, i.e. 16 years. The concentration of ions in groundwater would exceed background concentrations for up to 100 m at the end of 100 years. This study was used to predict the optimum chemical composition for the tailings and the extent, in terms of time and distance, that the groundwater concentration of various ions would be increased by infiltration of wastes from the tailings pond.     

Removal of Dissolved Arsenic by Pyrite Ash Waste

Pyrite ash (PA), a waste produced during the roasting of pyrite ores to produce sulfuric acid, was studied as a potential adsorbent for removing arsenic (As) from groundwater. The collected pyrite ash waste samples contained >86 % iron (as Fe₂O₃). The results indicate that adsorption of As by PA was only slightly affected by initial pH at pH ≤ 9. Arsenate removal efficiency increased with the amount of adsorbent added over the range of 0.1–50 g/L. The As(V) removal increased with time, and 79 % removal was achieved within 1 h. Moreover, there was no significant change in As concentrations after 24 h. The adsorption process was best described by a second-order kinetic model. The adsorption of As(V) onto the PA was found to have followed the Langmuir isotherm. In batch studies, the maximum As(V) removal efficiency was 97 % at an adsorbent dose of 10 g/L, with an initial As(V) concentration of 300 µg/L. Thus, the PA was shown to be a suitable sorbent, reducing As from an initial level of 600 to <10 μg/L As(V), i.e., below the WHO limit for drinking water.     

Removal of Metals and Acidity from Acid Mine Drainage Using Liquid and Dried Digested Sewage Sludge and Cattle Slurry

The metal removal and neutralization capacities of digested sewage sludges from municipal wastewater treatment plants, cattle slurry (liquid manure), and Biofert granules (dried granular anaerobic sludge) were compared under batch conditions using synthetic AMD (pH 2.8) containing high concentrations of Al, Cu, Fe, Mn, Pb, and Zn (100, 15, 270, 15, 2, and 30 mg/L, respectively). The effects of contact time and solids concentration were examined. Metal removal was variable for all materials. Contact time had a significant effect, with total removal often increasing over the experimental time interval (i.e. 30 min to 24 h). Removal efficiency (%) was generally highest for Cu, Pb, and Al, while Mn and Zn were the least removed. Cattle slurry was the best material for metal removal, with the following maximum removals at a solids concentration of 12.9 g/L: Cu >98 %, Al >98 %, Fe >60 %, Mn >18 %, Pb >96 %, and Zn >60 %. Metal removal using digested sewage sludge reached 88 % for Al, 98 % for Cu, 94 % for Pb, and 30 % for Zn. Neutralization was complete within 30 min after AMD was mixed with digested sludges or cattle slurry, with the pH reaching a maximum of 5.5 with the slurry. In contrast, neutralization by the Biofert granules only reached equilibrium after 300 min, and pH remained <4.0 except at high solids concentrations. It appears that recycled waste-derived organic materials can neutralize AMD and remove dissolved metals by adsorption and precipitation, creating a more treatable waste stream or one that could be discharged directly to surface water. Potential methods of safe disposal of metal-enriched organic materials are discussed.     

Oxidative Precipitation of Manganese from Dilute Waters

Various metals may be removed from mine water by precipitation of their hydroxides. However, over the pH range of 7–9, it is more efficient to oxidize Mn II to Mn IV than to precipitate Mn II as its hydroxide. Chlorine (or hypochlorite) can be used to do this, but its use may not be appropriate for mine waters that will be recycled as process solutions or discharged into a receiving body. Consequently, there has been interest in reducing chlorine use or its total replacement by non-chlorinated oxidants, such as oxygen and peroxygens, for treatment of mine water. In this work, we report the results of a comparative investigation of the following oxidants: NaClO (as reference), O₂; H₂O₂; Caro’s acid (H₂SO₅), and the combination of H₂O₂ with NaClO, with initial [Mn] = 10 mg/L, at 25 °C, with 100 and 300 % excess oxidant above the stoichiometric requirement. It was found that the reaction pH has to be greater than 8 to obtain effective precipitation. It is possible to reach a final [Mn] below 1.0 mg/L in 60 min of batch reaction time, using either NaClO, Caro’s Acid, or a combination of NaClO + H₂O₂. Using only O₂ or H₂O₂ was ineffective.