Influence of the slags treatment on the heavy metals binding

The removal of Cu(II) and Pb(II) was studied on two types of slags (blast furnace and steelmaking slag) and their modifications prepared by leaching with demineralized water (with contact time 24 and 48 h) and 0.001 mol L^?1 HCl solution. The slags and their modifications were characterized by x-ray fluorescence spectroscopy, x-ray diffraction, infrared spectroscopy, and the specific surface area was measured. Environmental scanning electron microscope was used to study the microscopic changes of the slags. The highest removal amounts of Cu(II) were found on the blast furnace slag leached for 48 h. This fact can be explained by the higher specific surface area of the leached blast furnace slag; the removal of Cu(II) is supposed to take place by co-precipitation of its hydroxides or hydroxo-complexes on the slag surface. On the contrary, the modified steelmaking slags exhibit no improvement of the removal properties. The used treatment of the slags decreased the sorption capacities for Pb(II). The original steelmaking slag showed to be the best adsorbent for both metal cations.     

广东云浮含Tl硫酸冶炼堆渣场土壤Tl污染的元素-Pb同位素示踪研究

利用元素总量和Pb同位素示踪技术对广东云浮硫酸厂含Tl黄铁矿冶炼堆渣场周围土壤中Tl的污染程度和迁移行为进行了研究。研究发现堆渣场周围土壤中Tl污染物主要集中于表层土壤约16．5cm深度内,并且表现出沿垂直方向向下迅速下降的特点。堆渣场周围土壤中Tl与Pb呈显著线性相关,表明自然条件下田与Pb在土壤中的迁移相似性,并且都以横向迁移为主。堆渣场固结层周围土壤至少44cm范围已经受到废渣中Tl释放的影响,Tl污染物平均下渗速率达到2．75cm／a。酸性雨水的淋滤作用及废渣自身不断酸化的特性是废渣中．Tl迁移释放入土壤的主要因素,土壤铁氧化物胶体及有机质是土壤对Tl产生吸附的主要载体。     

Mineralogical and geochemical controls on the release of trace elements from slag produced by base- and precious-metal smelting at abandoned mine sites

Slag collected from smelter sites associated with historic base-metal mines contains elevated concentrations of trace elements such as Cu, Zn and Pb. Weathering of slag piles, many of which were deposited along stream banks, potentially may release these trace elements into the environment. Slags were sampled from the Ely and Elizabeth mines in the Vermont copper belt, from the copper Basin mining district at Ducktown, Tennessee and from the Clayton silver mine in the Bayhorse mining district, Idaho, in the USA. Primary phases in the slags include: olivine-group minerals, glass, spinels, sulfide minerals and native metals for Vermont samples; glass, sulfide minerals and native metals for the Ducktown sample; and olivine-group minerals, clinopyroxenes, spinels, sulfide minerals, native metals and other unidentified metallic compounds for Clayton slag. Olivine-group minerals and pyroxenes are dominantly fayalitic and hedenbergitic in composition, respectively and contain up to 1.25 wt.% ZnO. Spinel minerals range between magnetite and hercynite in composition and contain Zn (up to 2.07 wt.% ZnO), Ti (up to 4.25 wt.% TiO₂) and Cr (up to 1.39 wt.% Cr₂O₃). Cobalt, Ni, Cu, As, Ag, Sb and Pb occur in the glass phase, sulfides, metallic phases and unidentified metallic compounds. Bulk slag trace-element chemistry shows that the metals of the Vermont and Tennessee slags are dominated by Cu (1900–13,500 mg/kg) and Zn (2310–10,200 mg/kg), whereas the Clayton slag is dominated by Pb (63,000 mg/kg), Zn (19,700 mg/kg), Cu (7550 mg/kg), As (555 mg/kg), Sn (363 mg/kg) and Ag (200 mg/kg). Laboratory-based leach tests indicate metals can be released under simulated natural conditions. Leachates from most slags were found to contain elevated concentrations of Cu and Zn (up to 1800 and 470 μg/l, respectively), well in excess of the acute toxicity guidelines for aquatic life. For the Idaho slag, the concentration of Pb in the leachate (11,000 μg/l) is also in excess of the acute toxicity guideline. Geochemical modeling of the leachate chemistry suggests that leachates from the Vermont, Tennessee and Clayton slags are saturated with amorphous silica and Al hydroxide. Therefore, the dissolution of silicate and oxide phases, the oxidation of sulfide phases, as well as the precipitation of secondary phases may control the composition of leachate from slags. The presence of secondary minerals on slag deposits in the field is evidence that these materials are reactive. The petrographic data and results of leaching tests from this study indicate slag may be a source of potentially toxic metals at abandoned mine sites.     

Beneficiation of a zinc-oxide rich phase by leaching refired Imperial Smelting Process slags

This paper deals with a method devised to concentrate and recover the zinc oxide present in Imperial Smelting Process slags. It is based on a preliminary refiring cycle, which enables the concentration of almost the whole of the zinc available in the slag in a newly formed phase, a magnetite—franklinite solid solution (Fe₃O₄ZnFe₂O₄), embedded in a glassy groundmass. The following sulphuric acid leaching treatment was found to exhibit a selective dissolving action, leaving most of the zinc-bearing phase as a solid residue.The laboratory procedure could be developed into a possible route for the complete utilization of Imperial Smelting Process slags.An overall recovery of about 85% of the total zinc available in the original slag was obtained after 8.5 hrs of leaching action of a 2% sulphuric acid solution at a temperature of 100°C.     

Carbon steel slag and stainless steel slag for removal of arsenic from stimulant and real groundwater

Arsenic in groundwater is a serious environmental problem. The contamination of groundwater with arsenic has been of utmost concern worldwide. Steel slag is a solid waste generated from steel production. Although steel slags have been used for arsenic removal from water, this process has not been systematically or integratively researched. In this study, the arsenic removal capacity and mechanism were investigated for carbon steel slag, stainless steel slag and Fe-modified stainless steel slag based on an in-depth study. The study also evaluated the potential utilization of different steel slag for regeneration. The maximum adsorption of arsenic on carbon steel slag, stainless steel slag and Fe-modified stainless steel slag was 12.20, 3.17 and 12.82 mg g^?1 at 25 °C, respectively. The modification of stainless steel slag by FeC1₃ can generate more pore structures and larger surface areas, and 300 °C treatment produces the best regeneration efficiency. The ΔG values were negative for all of the steel slags, indicating the spontaneous nature of the adsorption process. The solution pH was a critical parameter for the removal of arsenic for steel slags. Under highly alkaline solution conditions, the mechanism of arsenic removal by carbon steel slag and stainless steel slag can be attributed to chemisorption, including chemical precipitation and coordination reactions, and under weakly alkaline solution conditions, electrostatic interaction and specific adsorption are the arsenic removal mechanisms by Fe-modified stainless steel slag. Regeneration of the Fe-modified stainless steel slag was better achieved than that of the other steel slags in the application of high-temperature treatment.     

Comparison of Cu,Zn and Fe bioleaching from Cu-metallurgical slags in the presence of Pseudomonas fluorescens and Acidithiobacillus thiooxidans

Metal leaching from metallurgical wastes (slags) by means of environmentally friendly approaches is promising for practical applications. The goal of this study was to compare the feasibility of metal bioleaching from Cu slags by means of Pseudomonas fluorescens and Acidithiobacillus thiooxidans. Two size particles (<0.3 mm and 1–2 mm) of two types of Cu slags (massive crystalline slag and granulated amorphous slag) were used to study metal (Cu, Zn and Fe) bioleaching. The 40-days bioleaching experiments with P. fluorescens began at circumneutral pH (7.0), whereas the experiments with A. thiooxidans were started under acidic (pH 2.5) conditions. The results demonstrated that A. thiooxidans catalyzes metal leaching from both slag types investigated. After 21 days of incubation, optimal leaching was achieved and up to 79% Cu, 76% Zn and 45% Fe could be extracted from crystalline slag under conditions of 1 wt.% pulp density and particle size <0.3 mm. The optimal efficiency achieved with amorphous slag was 81% Cu, 79% Zn and 22% Fe when 1% pulp density and 1–2 mm particle size were used. The use of P. fluorescens resulted in poor leaching efficiencies as compared to the performance of A. thiooxidans, presumably due to the higher pH conditions maintained during the P. fluorescens incubations. The maximum metal leaching efficiencies with P. fluorescens were achieved at 1% pulp density and particle size <0.3 mm and did not exceed 10% Cu, 4% Zn, 0.3% Fe for crystalline slag and 4% Cu, 3% Zn, 0.7% Fe for amorphous slag. Both slags exhibited a good potential for bioleaching with A. thiooxidans, however; further optimization of the process parameters (e.g. pulp density, particle size and pH) is needed to improve the efficiency.     

黄铁矿利用过程中铊的迁移特征

以静态浸泡、动态模拟淋滤和逐级提取作基础,结合工艺过程,研究了黄铁矿利用过程中铊的迁移特征.结果表明,铊在焙烧时主要随飞灰和炉渣迁移,少量以 TlF的气态形式迁移;铊从飞灰、炉渣和沉灰渣中的释放率与浸泡时间成正比,与 Ph值和粒径成反比 (沉灰渣新样除外 ),且新样铊的释放率大于陈样,浸泡样品铊的释放率大于淋滤样品.当样品中可提取态铊含量较高,或飞灰中不可提取态铊含量较高,且飞灰含有 HF、 SO2和 SO3时,铊容易迁移.当赋存在碳酸盐矿物中的铊含量较高时,铊在酸性条件下也容易迁移,而保持炉渣和沉灰渣的 Ph值中性或接近中性,可有效防止废渣中的铊淋滤进入环境.     

Leaching of lead metallurgical slags and pollutant mobility far from equilibrium conditions

Lead metallurgical slags are partially vitrified materials containing residual amounts of Zn, Pb, Cr, Cd and As. These hazardous materials are generally buried on heaps exposed to weathering. In this study, leaching behavior of lead blast furnace slags has been tested using pure water and open flow experiments. It appears that in such far from equilibrium and slightly acidic conditions, the main phase to be altered is the vitreous phase. As for lunar, basaltic and nuclear glasses, alkalis/proton exchanges prevail and lead to the formation of a non-protective altered layer enriched in Si, Fe and Al. The composition of the altered layer is quite constant except for Si whose concentration decreases towards the leachate interface. Owing to their sizes, micrometric Pb droplets are not always totally dissolved at the slag surface. Nevertheless, nanometric Pb droplets are instantaneously dissolved while a surrounding altered layer is formed. This leads to high Pb releases in open flow systems. Leachate chemistry and dissolution rates of the vitreous phase are closely comparable to previous leaching tests with basaltic and nuclear glasses in conditions far from equilibrium. Moreover, this study confirms that Fe is a stable element in such conditions.     

Experimental investigation on shear strength and permeability of a deeply dewatered sewage sludge for use in landfill covers

This paper presents an experimental study on a deeply dewatered sewage sludge produced by using a new technique of membrane filter press. The experiments involve measurements of sludge composition, basic physical properties, shear strength, water permeability, and leaching toxicity. The measurements of shear strength and permeability were also performed on the sludge specimens soaked in a low acid leachate or distilled water for 1 and 2 months. This is to investigate the influence of chemical change in pore fluid as a result of rainfall infiltration or leachate seepage at landfills. Comparison tests were also carried out on silty clay that is commonly used for landfill cover material. The experimental results show that the deeply dewatered sludge contains 66 % organic content and 85 % water content (dry mass basis). The undrained shear strength of the sludge is >25 kPa even after 2-month soaking in the leachate and distilled water, meeting the requirement of the Chinese standard [CJ/T249-2007, Disposal of sludge from municipal wastewater treatment plant: sludge quality for co-landfilling. Ministry of Building and Construction, P.R. China (in Chinese), 2007]. The measured cohesion and friction angle for the sludge are >20 kPa and 22.3°, respectively. The soaking of sludge specimens in either leachate or distilled water resulted in an increase in frictional angle by several degrees. The water permeability for the sludge ranges from 0.68 × 10^?8 to 1.3 × 10^?8 cm/s, and permeability after 2-month soaking is less than the minimum requirement for the barrier layer of landfill covers (i.e., 1.0 × 10^?7 cm/s). The concentrations of heavy metals leaching from the dewatered sludge are lower than the limit values of leaching toxicity for the wastewater discharge standard of China. The experimental results indicate that deeply dewatered sludge can be used as an alternative material for the barrier layer of landfill covers.     

Utilization of Basic Oxygen Furnace (BOF) slag in the production of a hydraulic cement binder

Basic Oxygen Furnace (BOF) slag is a major waste product generated during the steelmaking process. In India and in most industrial countries, the use of BOF slag as a road ballast and land filler has had a very long history. This being a low end use, a study was conducted to examine the possibility of converting the slag into a hydraulic binder. This paper describes the effect of cooling rate on mineralogy and cementing characteristics of normal BOF slag as well as iron oxide-devoid BOF slag. Specifically, the mineralogy and compressive strengths of heat-treated slags were compared with a conventional ordinary Portland cement. It was found that the slowly cooled slags did not show any cementing properties. The iron oxide-devoid slag, on slow cooling, disintegrated into fine powder. The water-cured cubic specimens of quenched slag products were tested for their compressive strengths. The cementing properties of the quenched slag products were improved by formation of hydraulic phases and showed considerable strength after 28 days of water curing.     

Effectiveness of Mg–Al-layered double hydroxide for heavy metal removal from mine wastewater and sludge volume reduction

Health hazards from heavy metal pollution in water systems are a global environmental problem. Of similar concern is sludge that results from wastewater treatment due to unsatisfactory sludge management technology. Therefore, the effectiveness of using Mg–Al-layered double hydroxide in the removal of heavy metals from mine wastewater was tested and compared with that of calcium hydroxide [Ca(OH)₂], which is a common treatment method for heavy metal removal. Initially, the mine wastewater contained cations of the heavy metals iron (Fe), zinc (Zn), copper (Cu), and lead (Pb). The Mg–Al-layered double hydroxides were able to remove 371, 7.2, 121, and 0.4 mg/L of these pollutants, respectively, using the co-precipitation method. The removal of these metals is most effective using 0.5 g Mg–Al-layered double hydroxide (Mg/Al molar ratio 4) and 20 min of shaking. Zn was removed by the formation of Zn(NO₃)(OH)·H₂O and Zn₅(NO₃)₂(OH)₈ when LDH, Mg/Al molar ratios of 4 and 2, respectively, were used. Similarly, Fe, Cu, and Pb were removed by the formation of Fe–Al-layered double hydroxide, Cu₂(OH)₃·NO₃ and Pb₄(OH)₄(NO₃)₄, respectively. While Ca(OH)₂ is also capable of reducing the heavy metal concentrations below the Japanese recommended values, this analysis shows that using 0.5 g Mg–Al-layered double hydroxide is a better treatment condition for mine wastewater, because it generates lower sludge volumes than 0.1 g of Ca(OH)₂. The measured sludge volume was 1.5 mL for Mg–Al-layered double hydroxide and 2.5 mL for Ca(OH)₂, a nearly twofold further reduction.     

Evaluation of trace element availability from secondary metallurgical slag generated in steelmaking by sequential chemical extraction

During carbon steel manufacture, slag residues are generated to remove material impurities from liquid metal and thus control the quality of carbon steel. As the utilization of secondary metallurgical slags is not as efficient as those of primary slags, a comprehensive characterization of steel ladle slag was performed. Pseudo-total concentrations of a wide range of elements were determined during a 6-week sampling period with relevant physical and chemical properties, sequential extraction of trace elements, and parallel mineralogical characterization of extraction residues from a representative combined sample. According to the results, only Cr and V occurred in elevated concentrations with respective 6-week mean values of 198 and 310 mg kg^?1 (d.w.). The residual standard deviation of the weekly pseudo-total concentration values of the aforementioned elements (24 and 31 %, respectively) indicated that significant variation in the concentration of trace elements can occur due to fluctuation in process conditions and/or slag characteristics. The sequential extraction procedure suggested potential phytoavailability of V (123 mg kg^?1, d.w., amounting to 41 % of the respective pseudo-total concentration) through, e.g., changes in prevailing redox conditions. Although the analytical approach was validated by the analysis of a certified reference material and the calculation of extraction recoveries, the mineralogical characterization of parallel extraction residues indicated non-selectivity of the procedure coupled with potential redistribution phenomena during extraction with hydrogen peroxide and ammonium acetate.     

Rezente marine Eisenerze auf Santorin,Griechenland

Recent iron sediments forming at present in a bay of the volcanic island Palaea Kameni within the caldera of Santorini, Aegean Sea, have been investigated for their mineralogy and geochemistry. For the first time siderite has been found in a marine environment to be major constituent of a recent sediment. Further main constituents are opal, ferric hydroxide, vivianite, ferrous hydroxide, and possibly ferrous silicate. The chemical composition both of the solid material of the sediment cores and of their pore solution indicate that the ore forming solutions have originated from the leaching of volcanic kalk-alcaline rocks by hot acid solutions. This is in agreement with experimental leaching of these rock types. No enrichment of lead, copper, zinc etc. was found in the sediments. Iron oxidizing bacteria in the reddish-brown ferric hydroxide sediments now forming in bays of the Kameni Islands have been studied by light and electron microscopic investigations. Samples from the uppermost parts of the sediment consist mainly of the ferric hydroxide stalks of the iron bacteriumGallionella ferruginea. The stalks showing their morphological characteristics occur in such masses that there is no doubt concerning the presence, activity and share of these bacteria in the process of iron sedimentation. Phases of sedimentation process and kinetics of ferric hydroxide stalk formation have been determined qualitatively and quantitatively by in-situ-experiments using artificial growing surfaces (underwater “Aufwuchs” on glass slides). The results obtained are compared to similar iron sedimentation in fresh water habitats and iron rich carbonate springs discussed in literature in connection with the problem of submarine exhalative sedimentary iron ore formation.     

Environmental geochemistry and ecological risk of vanadium pollution in Panzhihua mining and smelting area, Sichuan, China

1 Introduction Vanadium (V) is a relatively abundant elemenwhich is widely distributed in nature; howeverworkable V deposits are very rare (World HealthOrganization, 2001). Vanadium is a trace elementwhich may be beneficial and possibly essential fohuman…     

Remediation of metal-contaminated soil in polar environments: Phosphate fixation at Casey Station,East Antarctica

Remediation of metal-contaminated soils by phosphate fixation is successful in temperate environments, whereas its efficacy in cold and freezing environments is understudied. Phosphate fixation is a low-cost technique and is potentially very useful in these remote environments where the logistics of remediation are difficult and expensive. Here we describe a field study at Casey Station, East Antarctica, where phosphate (triple superphosphate and phosphate rock) and a buffer, Emag (magnesium carbonate and magnesium oxide), were introduced to contaminated soil from nearby Thala Valley landfill. A pilot scale experiment was set up, sampled and monitored from December 2008 to February 2010. Relative to levels in the untreated landfill material, concentrations of Cd, Cu, Co, Fe, Mn, Pb and Zn in leachates were decreased by phosphate addition (fixation most effective for Mn and Zn), whereas the technique increased concentrations of As, Cr and Ni. The most successful fixation was found for the 3:2 ratio of triple superphosphate and Emag, and the least effective fixation occurred with the 2:1:1 ratio of triple superphosphate, Emag and phosphate rock. Although there was an undesirable initial flush of metals from the contaminated soil in the 24–48 h after treatment addition, concentrations in leachate were reduced and stabilised in the second summer. During a full-scale field implementation, complementary techniques would be required to contain and treat contaminated runoff until leachates have reduced to acceptable concentrations.     

Improvement in nitrification through the use of natural zeolite: influence of the biomass concentration and inoculum source

A batch nitrification process was studied using synthetic wastewater as substrate and Chilean natural zeolite as biomass carrier at ambient temperatures (20 °C). Three groups of experiments were carried out: a first experimental set (I) with and without added zeolite using initial biomass concentrations of 1,000 and 2,000 mg VSS/L; a second set of experiments (II) with added zeolite and at the same initial biomass concentrations. In these two experimental sets, biomass from an activated sludge process located in an urban wastewater treatment plant at La Farfana, Santiago de Chile, was used as inoculum (1). Finally, a third set of experiments (III) was carried out with zeolite at an initial biomass concentration of 1,000 mg VSS/L using an inoculum derived from an activated sludge process treating wastewater from a paper mill (inoculum 2). Nitrifying biomass concentration values in the range of 13,000–18,800 mg VSS/L were achieved when initial biomass concentrations varied between 1,000 and 2,000 mg VSS/L. Inoculum (1) generated higher biomass concentrations than inoculum (2). Ammonium N removals higher than 70 % were obtained in experimental sets II and III when zeolite was used. For both initial biomass concentrations tested, an exponential biomass growth was observed up to the second day of operation, and a slight decrease was evident afterwards, achieving stationary values after 10–12 days of operation. The third experimental set (III) revealed that the highest N consumption took place between days 11 and 16 of digestion.     

Mechanism of fluoride enrichment in groundwater of hard rock aquifers in Medak,Telangana State,South India

A total of 194 groundwater samples were collected from wells in hard rock aquifers of the Medak district, South India, to assess the distribution of fluoride in groundwater and to determine whether this chemical constituent was likely to be causing adverse health effects on groundwater user in the region. The study revealed that the fluoride concentration in groundwater ranged between 0.2 and 7.4 mg/L with an average concentration of 2.7 mg/L. About 57% of groundwater tested has fluoride concentrations more than the maximum permissible limit of 1.5 mg/L. The highest concentrations of fluoride were measured in groundwater in the north-eastern part of the Medak region especially in the Siddipeta, Chinnakodur, Nanganoor and Dubhaka regions. The areas are underlain by granites which contain fluoride-bearing minerals like apatite and biotite. Due to water–rock interactions, the fluoride has become enriched in groundwater due to the weathering and leaching of fluoride-bearing minerals. The pH and bicarbonate concentrations of the groundwater are varied from 6.6 to 8.8 and 18 to 527 mg/L, respectively. High fluoride concentration in the groundwater of the study area is observed when pH and the bicarbonate concentration are high. Data plotted in Gibbs diagram show that all groundwater samples fall under rock weathering dominance group with a trend towards the evaporation dominance category. An assessment of the chemical composition of groundwater reveals that most of the groundwater samples have compositions of Ca²⁺–Mg²⁺–Cl^? > Ca²⁺–Na⁺–HCO₃ ^? > Ca²⁺–HCO₃ ^? > Na⁺–HCO₃ ^?. This suggests that the characteristics of the groundwater flow regime, long residence time and the extent of groundwater interaction with rocks are the major factors that influence the concentration of fluoride. It is advised not to utilize the groundwater for drinking purpose in the areas delineated, and they should depend on alternate safe source.     

Mechanical Behavior and Sulfate Resistance of Alkali Activated Stabilized Clayey Soil

Clayey subgrade soil requires treatment in order to make the subgrade stable for pavement structures. Treatment of clayey soil i.e. stabilization of clayey soil by cement, lime, and fly ash are established techniques used in geotechnical and highway engineering. Stabilization by alkali activation of fly ash is reported recently but literatures are limited. Present study investigates the stress strain behavior, peak stress and ultimate strain of clayey soil stabilized by slag and slag-fly ash blending by alkali activation. The peak stress as high as 25.0 N/mm² may be obtained at 50% slags content when 12 molar sodium hydroxide solutions were used. Peak stress, ultimate strain and slope of stress–strain curve of stabilized clay are controlled by Na/Al and Si/Al ratios. Stress–strain response and peak stress of slag and fly ash blended specimen are not governed by Na/Al and Si/Al ratios; rather the behavior is dependent predominantly on slag content.     

A new technique for extracting zirconium form Egyptian zircon concentrate

Zircon is the most important commercial source of zirconium, its compounds and alloys. Several methods are used for industrial processing of zircon for production of zirconium dioxide and tetrachloride. These methods include sintering of zircon with sodium carbonate or sodium hydroxide or calcium oxide or calcium carbonate and with potassium fluorosilicate, chlorination of zircon mixture with coal in blast furnace and carbidization of zircon in a mixture of coal in electric arc furnace. All these methods are carried out at high temperatures and have many disadvantages.The present work illustrates a study of a new technique for extracting zirconium from Egyptian zircon concentrate by its simultaneous ball-milling and pressure alkaline leaching, to improve the recovery of zirconium from zircon. Experiments were carried out in stainless steel ball-mills of cylindrical shape under different conditions of temperature, pressure and time. The ball-mills were heated and mechanically rotated in an electric furnace by means of roll mechanism.The filtrate after leaching of zircon, containing excess of sodium hydroxide was regenerated by its treatment with calcium hydroxide for purification from silicon impurity. Then, the solution was evaporated to the desired concentration (500 g/l Na₂O) and recycled to the reactor of leaching.The results obtained show that complete recovery of zirconium from zircon (99.7%) by simultaneous ball-milling and alkaline leaching was attained at 250 °C within 3 h, using amount of sodium hydroxide 150% of theoretical requirement (satisfying favourable conditions of zirconate cake for subsequent acid leaching).The standard free energy (ΔF^o) and equilibrium constant (K) of the reaction of zircon with sodium hydroxide were calculated as—19.58 k cal mol^− 1 and 2.29 · 10¹⁴, respectively. The kinetics of the technological alkaline processing of zircon in ball-mall autoclaves was studied over the temperature range 150–275 °C.     

Heavy metal chemical fractionation and immobilization in lightweight aggregates produced from mining and industrial waste

The fractionation of five heavy metals in a washing aggregate sludge, a sewage sludge, a clay-rich sediment, the mixtures of these materials and the lightweight aggregates manufactured with them has been determined by applying the optimized European Community Bureau of Reference sequential extraction procedure in order to evaluate the effects of the heating process on the extraction of these elements. Additionally, preparation of eluates by aggregate leaching has been performed in accordance with the UNE-EN-H44-3 standard. The availability of all the studied heavy metals has been reduced by the thermal treatment, since most of the heavy metals have become part of the undigested material in the lightweight aggregates. Nickel has been the heavy metal that has presented the highest concentration in the eluates obtained after completion of the single extraction procedure in the lightweight aggregates. The studied lightweight aggregates may be used in lightweight concrete manufacturing from the standpoint of heavy metal leaching.