Impact of organic carbon on the leachability of vanadium,manganese, iron and molybdenum from shale residues

From 1942 to the 1966, oil was produced by pyrolysis of shale, in Kvarntorp, Sweden. This generated some 40 million m³ of metal rich pyrolyzed shale and discarded fines that were piled on site with its original metal content almost intact. The present study focuses on the leaching of vanadium, manganese, iron and molybdenum from fines after addition of wood chips and steel slag, in outdoor 1 m³ reactor systems at low liquid to solid ratio, in order to evaluate the potential environmental impact and recovery of the elements from the leachates. Seasonal variations were observed, with increased leaching during peak summer. For vanadium and molybdenum, high addition of wood chips decreased the leaching, probably due to adsorption. Manganese showed the opposite behavior while leaching of iron was almost independent of the amount of wood chips. Depending on the systems, up to 2200 μg L⁻¹ vanadium, 90 μg L⁻¹ molybdenum, 25 mg L⁻¹ manganese and 500 mg L⁻¹ iron was found in the aqueous phase. Applied to the 40 million m³ pile, the annual leaching of those elements may reach 14 ton, 0.6 ton, 200 ton and 2400 ton, respectively.     

Selective flotation of cassiterite with benzohydroxamic acid

The flotation of cassiterite mineral from gangue with a collector benzohydroxamic acid (BHA), and the interactions between the BHA and cassiterite have been investigated. It is shown through microflotation that the BHA is able to flot cassiterite very well, calcite quite limitedly, and quartz not at all, so the selective separation of cassiterite–quartz mixture was readily achieved; while for the efficient separation of cassiterite–calcite mixture containing 48.94% SnO₂, sodium hexametaphosphate (SHMP) was needed as a depressant for the gangue, and under the condition of the BHA 100 mg L⁻¹, SHMP 3.5 mg L⁻¹, a cassiterite concentrate with the grade of 85.50% SnO₂ was obtained with the recovery of SnO₂ 95.5%. Batch flotation further demonstrated that for an industrial tin slime, which contained 0.42% Sn, 13.65% SiO₂, 24.14% CaO, 16.60% MgO, 4.50% Al₂O₃ and 6.58% Fe, the tin recovery of 84.5% after one separation was reached with the concentrate grade of 1.84% Sn under the condition of the BHA 178 mg L⁻¹, SHMP 27 mg L⁻¹. In terms of zeta potential and infrared spectra studies the main interactions between the collector BHA and the mineral cassiterite in a flotation system are chemisorption with the formation of Sn–BHA compounds rather than electrostatic attractions between them.     

Simultaneous determination of Au(III) and Cu(II) with 1-phenyl-1,2-propanedione-2-oximethiosemicarbazone (PPDOT) on solid phase

A new method for the simultaneous determination of copper and gold was developed by derivative spectrophotometry using a previous preconcentration on solid phase. The method is based on the formation of Cu(II)-PPDOT and Au(III)-PPDOT complexes that are extracted from aqueous solution in only 20 min on cationic exchange SP Sephadex C25. In this simultaneous determination, the second derivative and the zero crossing method were used. The copper and gold determinations were carried out at 278.0 nm and 282.0 nm, respectively. The determination range for both analytes was 1.6 × 10⁻⁸–141 × 10⁻⁸ mol L⁻¹. Good levels of repeatability (RSD) of 1.3% and 1.4% were observed for copper and gold, respectively. The method was applied successfully for the copper and gold determination in mineral residuals, minerals and natural water samples. The results were consistent with those provided by ICP-mass spectrometry.     

Zinc precipitation by heavy-metal tolerant sulfate-reducing bacteria enriched on phosphogypsum as a sulfate source

In the present study, heavy-metal tolerance and precipitation by a mixed culture of sulfate-reducing bacteria (SRB) were evaluated. These bacteria have been enriched during a previous study from a sewage sludge using phosphogypsum as sulfate source. Taking into account that both sulfate and zinc are naturally occurring in phosphogypsum, zinc tolerance of SRB was tested in synthetic media containing 20 mM sulfate and zinc chloride at concentrations ranging from 0 to 200 mg L⁻¹. Zinc tolerance was determined by bacterial growth susceptibility and zinc removal monitoring. Bacterial growth and sulfate reduction were possible between 10 and 150 mg L⁻¹ of initial zinc concentration. Zinc concentrations more than 150 mg L⁻¹ were lethal to SRB. Zinc was removed effectively by SRB to less than 5% from medium containing 150 mg L⁻¹ initial zinc concentrations or less. Energy-dispersive X-ray analysis showed that precipitation of zinc occurred in the form of sulfide. The results presented in this paper have shown that this mixed culture might be of use for bioremediation of sulfate and heavy-metals containing wastewaters.     

Zinc removal in anaerobic sulphate-reducing liquid substrate process

Zinc and sulphate removal from synthetic wastewater was investigated by using four laboratory parallel upflow-mode reactors (referred as R1 to R4; R1 contained carriers to retain biomass, whereas R2–R4 were operated as suspended reactors). All reactors were inoculated with anaerobically digested cow manure. R1 and R2 were first fed with glucose- and sulphate-containing feed for 48 days after which all four reactors were fed with wastewater containing 50 mg l⁻¹ of zinc in R1–R3 and 200 mg l⁻¹ in R4 and operated for 96 days. In all reactors, hydraulic retention time, organic loading rate, and sulphate load were 5–6 d, 0.2–0.4 kg COD m⁻³ d⁻¹ and 3.3–3.8 g SO₄ l⁻¹ d⁻¹, respectively, whereas the zinc load in R1–R3 was 0.074–0.077 and in R4 0.282 g Zn l⁻¹ d⁻¹. During the runs, 30–40% of sulphate and over 98% of zinc was removed, and up to 150–200 mg H₂S was produced in all reactors. Effluent pH dropped in all reactors (feed pH 6.5) to 3–5 by the end of the experiment. No significant effects on zinc removal were observed, despite differences in operating conditions and feed. It was only in the latter part of the runs (i.e. between experiment days 120–142) that zinc removal began to fluctuate, showing a negligible decrease in R3 and R4, whereas in R1 and R2 zinc was removed below the limit of detection (<0.01 mg Zn l⁻¹). Qualitative X-ray diffraction analysis of the reactor sludge at the end of the runs indicated that the compounds precipitated were most probably ZnS (Code 05-0566 Sphalerite), suggesting metal removal through sulphide precipitation; this was supported by the fact that sulphate was reduced and zinc removed simultaneously.     

A simple spectrophotometric method for determination of gold (III) in aqueous samples

A simple method for rapid determination of trace Au in natural water was presented by using UV–vis spectrophotometry after reaction of gold (III) with 3,3′, 5,5′-tetramethylbenzidine hydrochloride (TMBH) in acidic solution. Under the optimum conditions, in a concentration range of 100–2000 μg L^?1 of Au (III) a good linear calibration graph was obtained (r = 0.9969, n = 7). The percent relative standard deviation (RSD) for determination of 1000 μg L^?1 Au was 10% (n = 3) and limit of detection based on a signal-to-noise ratio (S/N) of 3 (3S_bl) was 50 μg L^?1. The proposed method has been successfully applied to the determination of gold spiked and real aqueous samples.     

Leaching of chalcopyrite (CuFeS2) with an imidazolium-based ionic liquid in the presence of chloride

The effects of independent variables such as, temperature, concentration of ionic liquid (1-butyl-3-methyl-imidazolium hydrogen sulphate, [bmim][HSO₄]), chloride and sulphuric acid on copper extraction from chalcopyrite (CuFeS₂) ore were studied by surface optimization methodology. The Central Composite Face approach and a quadratic model were applied to the experimental design. The optimal copper extraction conditions given by the above methodology were 20% (v/v) of [bmim][HSO₄] in water, 100 g L⁻¹ chloride, and 90 °C. The concentration of chloride and the temperature together exert a synergistic effect in enhancing chalcopyrite dissolution. Experimental data were fitted by multiple regression analysis to a quadratic equation and analyzed statistically. A model was developed for predicting copper extraction from CuFeS₂ ore with variables such as Cl⁻, [bmim][HSO₄], H₂SO₄ concentrations and temperature in the range studied. The activation energy was calculated to be 60.4 kJ/mol (temperature range 30–90 °C), indicative of chemical control of the reaction and [bmim][HSO₄] acts as an acid in the reaction.     

Single and binary component sorption of the fission products Sr2+, Cs+ and Co2+ from aqueous solutions onto sulphate reducing bacteria

This study investigates the removal of the fission products Sr²⁺, Cs⁺ and Co²⁺ in single and binary metal solutions by a sulphate reducing bacteria (SRB) biomass. The effect of initial concentration and pH on the sorption kinetics of each metal was evaluated in single metal solutions. Binary component equilibrium sorption studies were performed to investigate the competitive binding behaviour of each metal in the presence of a secondary metal ion. Results obtained from single metal equilibrium sorption studies indicated that SRB have a higher binding capacity for Sr²⁺ (q_max = 416.7 mg g^?1), followed by Cs⁺ (q_max = 238.1 mg g^?1), and lastly Co²⁺ (q_max = 204.1 mg g^?1). Among the binary systems investigated, Co²⁺ uptake was the most sensitive, resulting in a 76% reduction of the sorption capacity (q_max) in the presence of Cs⁺. These findings are significant for future development of effective biological processes for radioactive waste management under realistic conditions.     

Sodium isopropyl xanthate degradation by advanced oxidation processes

This paper presents the results obtained by different oxidative processes when an aqueous solution containing sodium isopropyl xanthate is treated; this reagent is used in the flotation of copper minerals. The advanced oxidation processes used are UV photolysis, direct electrolysis and photoelectrooxidation. The solutions used containing sodium isopropyl xanthate were adjusted to the following concentrations: 6, 8, 10, 25 and 40 mg L⁻¹. The results show that the three oxidation processes proved to be suitable for the destruction of xanthate, with the following maximum destruction efficiencies: 76% for electrolysis, 95% for UV photolysis and 99% for photoelectrooxidation.     

Effects of quartz addition on chalcopyrite bioleaching in shaking flasks

This paper studies the effects of quartz on bioleaching of chalcopyrite by Acidithiobacillus ferrooxidans, LD-1 through shaking flask experiments. The results showed that quartz concentration can affect the copper extraction. After 32 days, copper extraction of the leaching system at 50 g L⁻¹ quartz concentration increased by about 20%, compared with that of the leaching system without quartz. XRD analysis showed that the amounts of jarosite on the chalcopyrite surface may reduce by the mechanical friction action between fine particles of quartz and chalcopyrite. The analysis of SEM indicated that the surfaces of chalcopyrite particles were eroded by different degrees and the degrees of change were the same as the effects of quartz concentration on copper extraction.     

Simultaneous oxidation and immobilization of arsenite from refinery waste water by thermoacidophilic iron-oxidizing archaeon,Acidianus brierleyi

The use of a thermophilic acidophilic iron-oxidizing archaeon, Acidianus brierleyi, was investigated for oxidation and immobilization of As(III) from acidic refinery waste water. Some As(III) oxidation was measured in all Ac. brierleyi cultures independently of the presence or concentration of Fe(II) in bulk solution; the exception was at initial Fe(II) concentration ([Fe(II)]_ini) of 1000 mg l⁻¹ where As(III) oxidation became markedly facilitated and consequently approximately 70% of As was immobilized as amorphous ferric arsenate. Providing 1000 mg l⁻¹ Fe(III) instead of Fe(II) did not show the same effect, implying the importance of Fe(III) be microbially-produced and complexed in the archaeal EPS (extracellular polymeric substances) region for effective As(III) oxidation. The reaction towards secondary mineral formation shifted from ferric arsenate to jarosite at [Fe(II)]_ini of >1000 mg l⁻¹. Furthermore addition of jarosite seed crystals retarded the As(III) oxidation rate at [Fe(II)]_ini of 1000 mg l⁻¹. The observations indicate that by setting the appropriate bulk Fe(II)/As(III) ratio in Ac. brierleyi culture to achieve a certain concentration of Fe(III) within the EPS region, but at the same time to avoid jarosite formation, it is possible to maximize the As(III) oxidation rate and thus As immobilization efficiency. This study describes for the first time microbially-mediated simultaneous oxidation and immobilization of As(III) as ferric arsenate, using a thermoacidophilic iron-oxidizing archaeon, Ac. brierleyi.     

Multicolumn solid phase extraction with hybrid adsorbent and rapid determination of Au,Pd and Pt in geological samples by GF-AAS

A novel hybrid adsorbent (HA) composed of cellulose fiber, activated carbon, and anion exchange resin Dowex 1 × 8 was prepared for the preconcentration and separation of noble metals, namely, gold (Au), palladium (Pd) and platinum (Pt), in geological samples. The optimal experimental parameters, such as flow rate, sample volume and interfering ions, were investigated. The accuracy of the method was confirmed by added/found method for tap and sea water, and evaluated by analyzing certified reference materials with good agreement. Under the optimal experimental conditions, the detection limits (3σ criteria) of the developed technique were 0.008 ng mL⁻¹ (Au), 0.017 ng mL⁻¹ (Pd) and 0.014 ng mL⁻¹ (Pt) and the sample throughput reach to 30 samples every eight hours. Moreover, the adsorption capacity of HA for Au, Pd and Pt was determined to be 48.2, 35.9 and 29.8 mg g⁻¹, respectively.     

Process development for the recovery of europium and yttrium from computer monitor screens

This work describes the development of a process for the recovery of Eu and Y from cathode ray tubes (CRTs) of discarded computer monitors with the proposition of a flow sheet for the metals dissolution. Amongst other elements, europium and yttrium are presented in the CRTs in quantities – 0.73 w/w% of Eu and 13.4 w/w% of Y – that make their recovery worthwhile. The process developed is comprised of the sample acid digestion with concentrated sulphuric acid followed by water dynamic leaching at room temperature. In the CRTs, yttrium is present as oxysulphide (Y₂O₂S) and europium is an associated element – Y₂O₂S:Eu³⁺ (red phosphor compound). During the sulphuric acid digestion, oxysulphide is converted into a trivalent Eu and Y sulphate, in solid form, with the liberation of H₂S. In the second step, metals are leached from the solid produced in the acid digestion step by dynamic leaching with water. This study indicates that a proportion of 1250 g of acid per kg of the sample is enough to convert Eu and Y oxysulphide into sulphate. After 15 min of acid digestion and 1.0 h of water leaching, a pregnant sulphuric liquor containing 17 g L⁻¹ Y and 0.71 g L⁻¹ Eu was obtained indicating yield recovery of Eu and Y of 96% and 98%, respectively. Both steps (acid digestion and water leaching) may be performed at room temperature.     

Determination of specific heat capacity of sulphide materials at temperatures below 100 °C in presence of moisture

The specific heat capacity (C_p) of one copper and three nickel concentrates was determined using a self-heating apparatus and by drop calorimetry over the temperature range 50 to 80 °C in the presence of 6% moisture. The C_p values from both techniques were comparable and shown to be measuring the same property. The C_p values were similar for all four concentrates increasing from ca 0.4 to 1.4 J g⁻¹ K⁻¹ as temperature increased from 50 to 80 °C. Uses of C_p to identify self-heating risk and to modify the Rosenblum standard test are discussed.     

Heavy metals removal from solution by palygorskite clay

The possible use of palygorskite clay, mined in the Dwaalboom area of the Northern Province of South Africa, as an adsorbent for the removal of metal ions such as lead, nickel, chromium and copper from aqueous solution, was investigated. In this work, adsorption of these metals onto palygorskite has been studied by using a batch method at room temperature. The results of adsorption were fitted to both the Langmuir and Freundlich models. Satisfactory agreement between experimental data and the model-predicted values was expressed by the correlation coefficient (R²). The Langmuir model represented the sorption process better than the Freundlich one, with correlation coefficient (R²) values ranging from 0.953 to 0.994. The adsorption capacity (Q₀) calculated from the Langmuir isotherm was 62.1 mg Pb(II) g⁻¹, 33.4 mg Ni(II) g⁻¹, 58.5 mg Cr(VI) g⁻¹ and 30.7 mg Cu(II) g⁻¹ at a pH of 7.0 at 25 ± 1 °C for a clay particle size of 125 μm. Kinetic investigations were performed to investigate the rate of adsorption of metal ions. The Lagergren’s first-order rate constants were calculated for different initial concentrations of metal ions. In batch mode adsorption studies, removal increased with an increase of contact time, adsorbent amount and solution pH. Adsorption of metals from the single-metal solutions was in the order: Pb > Cr > Ni > Cu. Data from this study proved that metal cations from aqueous solution can be adsorbed successfully in significant amounts by palygorskite. This opens up new possibilities and potential commercial uses in the palygorskite market.     

Application of ocean manganese nodules for the adsorption of potassium ions from seawater

Extracting potassium from seawater has great economic potential, although conventional methods offer low separation capacity and selectivity. In this study, a series of novel potassium ionic sieves (PISs) were synthesized using ocean manganese nodules (OMN) as raw materials. The PISs were characterized by XRD, SEM, and nitrogen adsorption–desorption. The potassium adsorption capacities and separation factors of PISs and OMN in KCl solution and sea brine showed that KMnO₄ treatment will result in the highest adsorption and separation performance. The resulted sample OMN-C exhibit major composition of birnessite-type potassium manganese oxides and high micropore volumes. The adsorption capacities of OMN-C to K⁺ in KCl solution and sea brine were 35.2 mg g⁻¹ and 22.1 mg g⁻¹, respectively. The separation factor of OMN-C was α(K⁺/Na⁺) = 108.6 and the sieve did not adsorb Mg²⁺, indicating its relatively high separation selectivity to K⁺. Therefore, OMN-C can selectively extract potassium from sea brine effectively. This study not only utilized the abundant OMN resources, but also prepared effective PISs, which showed great potential in the utilization of seawater.     

Review of rate constants for thiosulphate leaching of gold from ores,concentrates and flat surfaces: Effect of host minerals and pH

A review of literature data for different types of sulphide concentrates and gold ores has been carried out to examine the impact of host minerals and pH upon gold leaching. Analysis of initial rate data over the first 30–60 min of gold leaching from sulphide concentrates or silicate ores over a range of ammonia, thiosulphate, and copper(II) concentrations, pH (9–10.5) and temperatures up to 70 °C shows the applicability of a shrinking sphere kinetic model with an apparent rate constant of the order k_ss = 10⁻⁶–10⁻³ s⁻¹. The dependence of apparent rate constant on pH and initial concentrations of copper(II) and thiosulphate is used to determine a rate constant k_Au(ρr)⁻¹ of the order 1.0 × 10⁻⁴–7.4 × 10⁻⁴ s⁻¹ for the leaching of gold over the temperature range 25–50 °C (ρ = molar density of gold, r = particle radius). These values are in reasonable agreement with rate constants based on electrochemical and chemical dissolution of flat gold surfaces: k_Au = 1.7 × 10⁻⁴–4.2 × 10⁻⁴ mol m⁻² s⁻¹ over the temperature range 25–30 °C. The discrepancies reflect differences in surface roughness, particle size and the effect of host minerals.     

Iron redox-equilibria and sulphide capacity of PGM melter-type slags

New measurements have been made on the ferric to ferrous ratio as well as the sulphide capacity for platinum group metals (PGM) melter-type slags. In South Africa, these slags are produced from the smelting of low-grade copper–nickel sulphide ores, Nell [Nell, J., 2004. Melting of platinum group metal concentrates in South Africa. The South African institute of Mining and Metallurgy 104 (7), 423–428]. The typical mass compositions are 5–10% Al₂O₃, 2–15% CaO, 5–30% FeO_x, 15–25% MgO and 40–60% SiO₂ with a molar basicity defined as (CaO + MgO)/SiO₂ of 0.6–1. The industrial furnaces operate at temperatures ranging from 1450 to 1600 °C under fairly reducing conditions (typically a pO₂ close to 10⁻⁸ atm at 1500 °C). The gas–slag equilibrium was studied by subjecting a synthetic slag to controlled atmospheres in a vertical tube-furnace using Ar–CO–CO₂ (–SO₂) gas mixtures. The ratio of ferric to ferrous was determined at 1450 °C for oxygen activities, defined as pCO₂/pCO, ranging from 0.11 to 1.75 by analysing the quenched slags using the standard titration and XRF techniques. The measured Fe³⁺/Fe²⁺ ratio increased from 0.029 to 0.110 with the increasing oxygen activity. Slight non-ideal iron redox behaviour was observed, as has been reported for low alumina and low iron-containing slags. The present results are in good agreement with the trends found in the literature for similar multi-component slag systems (mostly iron bath smelting slags). Sulphide capacity was measured at partial pressures of oxygen and sulphur of approximately 10⁻⁹ and 10⁻³ atm respectively, with total-iron contents of 8.2 and 15.6 wt%, and temperature ranging from 1450 to 1525 °C. The present sulphide capacity data ranged from 10^−4.43 to 10^−3.71. The expected increase in sulphide capacity with increasing temperature was observed, and at a given temperature, the sulphide capacity increased with an increase in iron oxide content.     

Pulse electrodeposition as a new approach in electrowinning of high purity cobalt from WC–Co scraps. Part I: The effect of frequency and duty cycle

The high price of cobalt is the reason for the necessity of its recovery from recycled cutting tools, catalysts and so forth. In this research, the effect of frequency and duty cycle in pulse electrowinning of cobalt from WC–Co scraps has been studied. The scraps was first dissolved in a solution containing 1 N hydrochloric acid and 0.1 M citric acid in anodic potential in the range of 0.05–0.3 V_Ag/AgCl so that a solution with 22 g L⁻¹ cobalt was acquired. Electrodeposition was performed on a stainless steel cathode in frequencies of 30, 50, 70, 100 and 135 Hz; duty cycles of 10%, 30% and 50%; and peak current density of 250 A m⁻²; and electrolyte temperature of 60 °C. The surface of the deposits was observed with SEM and its purity was measured using the ICP method. The studies showed that increased frequency reduces the crystal size and the purity of the deposit increases up to 99.1 wt% under the same conditions. Increasing the duty cycle raises the cobalt crystal size and the highest purity of deposit is obtained at a duty cycle of 30%. The optimum conditions in terms of economics and purity involve electrodeposition at a frequency of 70 Hz and duty cycle of 30%, where deposits with a purity of 94.13 wt% are obtainable.     

Adsorbing flocs in expanded/fluidised bed reactors: A new basis for pollutants removal

The present work describes studies concerning a new adsorption technique based on the use of adsorbent flocs in an expanded/fluidised bed reactor for the removal of pollutants from aqueous solutions. The technique, based on flocculation of aqueous suspensions of powdered adsorbent materials, when conducted in an expanded/fluidised bed reactor takes advantage of conducting adsorption and solid–liquid separation in one single stage. Studies were performed using flocculated powdered activated carbon and natural zeolites, alone and in mixtures, for phenol and ammonia adsorption. A reactor with cylindrical–conical geometry was used for the pollutants adsorption in flocs beds (pure and mixed), as well as the regeneration/recycle of the exhausted adsorbents. Results proved the high adsorption efficiency of powdered natural zeolites and activated carbon flocs for the uptake of ammonia (11 mg NH₃–N g⁻¹) and phenol (132 mg g⁻¹), at 38 and 19 m h⁻¹ loading rates, respectively. Regeneration/recycle of the pollutant-saturated beds was possible for the ammonia/natural zeolites adsorption case, using sodium sulphate as regenerator. Use of mixed flocs beds was efficient, showing advantages such as multiple-pollutants adsorption in one single stage, higher loading rates when using light materials (activated carbon) combined with heavier ones (natural zeolites) and use of small adsorbent concentrations (not possible otherwise). Economical and environmental issues regarding the technique are also discussed in the paper. The new technique shows great potential as an alternative physicochemical adsorption process for pollutant removal from aqueous solutions using low-cost and highly-available powdered adsorbent materials.