Recovery Of Cr Research Articles

An environmentally benign process for effective recovery and solidification of Cr from stainless-steel slag

Stainless-steel slag is a hazardous solid that has caused severe chromium contamination globally. This study proposes an environmentally benign vitrification process for efficient recycling and solidification of Cr from stainless-steel slag using waste copper slag and coal tar residue. The transformation behaviors of heavy metals (Cr, Cu, Pb, Zn) and the Cr toxic leaching mechanism are also determined in this work. The findings indicated that compared with Cu and Fe phases, the Mg(Al,Cr)2O4 and chemically dissolved Cr phases were not easily reduced via coal tar residue, leading to the leaching of highly toxic Cr3+/Cr6+ during the toxicity characteristic leaching procedure (TCLP). Under optimal conditions, 95.56% Cr, 97.71% Fe, and 99.71% Cu could be recovered in the form of high value-added crude stainless-steel, and 99.62% Pb and 99.19% Zn could be enriched in the dust. The furnace slag TCLP result indicated that the leaching concentrations of Cr, Cu, Pb and Zn were 1.82 mg/L, 0.1 mg/L, 0.38 mg/L, and 2.58 mg/L, respectively. More importantly, the concentrations of residual Cr, Cu, Pb and Zn in the furnace slag were only 0.095 wt%, 0.028 wt%, 0.0192 wt%, and 0.011 wt%, respectively. These findings indicate that treated slag can be categorized as general solid waste, minimizing the environmental risks of heavy metals. The results of this study are significant for the sustainable development of the stainless-steel industry and copper metallurgy.

A metallurgical approach for separation and recovery of Cu, Cr, and Ni from electroplating sludge

Electroplating sludge is extensively produced in chemical precipitation–based treatment of electroplating wastewater. It poses a huge threat to environmental safety if not properly disposed, ascribed to its high contents of heavy metals. An innovative metallurgical approach was proposed a to recycle Cu, Cr, and Ni from it. Ammonia leaching was firstly performed to selectively leach Cu from Cr, in which the Cu oxide and sulfide were leached into the leachate while the Cr oxide and Ni carbide (NiCx) retained in the residue. (NH4)2SO4 increased the Cu leaching rate via increasing the dissolved oxygen amount in the ammonia leachate and converting CuS to Cu2+. Under the optimal conditions, the leaching efficiency of Cu achieved 96.5 % while that of Cr was only 0.1 %. In the followed aluminothermic reduction, C in the leaching residue could be effectively removed via a thermal oxidation, which in turn decreased the formation of a C-containing compound of high melting point and benefited the Cr and Ni recovery. Cr and Ni from the residue were reduced and recovered in a Cr-Ni alloy, and the reductant of Al first changed to a refractory Al2O3 and then transformed to a low melting point 12CaO·7Al2O3 with the additive of CaO. This transformation increased the molten slag fluidity and promoted the separation of Cr-Ni alloy from slag. Moreover, the excessive Al increased the Cr and Ni yields and concentrated all of them to be together. Partial Al was used as reductant, and the other Al transferred into Cr-Ni alloy to decrease its melting point. Cr and Ni contents in the smelting slag could be decreased to 0.11 wt% and 0.12 wt% respectively, showing an efficient recovery. This work provided a high efficiency method to recover Cu, Cr, and Ni from waste electroplating sludge.

The Direct Alloying of Steel through Silicothermic Self-Reduction of Chromite Ore Utilizing Si-Containing Solid Waste

Organosilicon materials generate copious amounts of Si-containing solid waste during production, leading to severe environmental pollution and substantial resource squandering. In pursuit of the resource utilization of Si-containing solid waste, this study conducted experimental research on the direct alloying of molten steel through the silicothermic self-reduction of chromite ore using Si-containing solid waste as a reducing agent. Additionally, thermodynamic analysis was performed, employing the thermodynamic calculation software FactSage 8.2 (Thermfact Ltd., Montreal, QC, Canada and GTT-Technologies, Aachen, Germany), to examine the equilibrium reactions of the silicothermic reduction of chromite ore and the variations in the thermodynamic equilibrium compositions of slag and metal phases. The results indicate a reduction sequence for the reducible components in chromite ore as Fe2O3 → Cr2O3. The introduction of CaO and Al2O3 into the silicothermic self-reduction compacts altered the forms of Fe and Cr oxides in equilibrium, significantly reducing the standard Gibbs free energy (ΔG0) of the silicothermic reduction reaction. The initial slag melting point decreased from 1700 °C without the addition of CaO and Al2O3 to 1500 °C with the addition of CaO and Al2O3. Correspondingly, the slag viscosity at 1600 °C decreased from 134.1 Pa·s without CaO and Al2O3 addition to 1.81 Pa·s with CaO and Al2O3 addition. The addition of CaO and Al2O3 accelerated the reduction of Cr oxide in chromite ore and enhanced the recovery of Cr, consistent with the thermodynamic calculation results. In the process of steelmaking through the direct alloying of chromite ore silicothermic self-reduction compacts, the final recovery rate of Cr increased from 86.4% without CaO and Al2O3 addition to 95.4% with CaO and Al2O3 addition.

Adsorption Studies on Red Mud: Removal and Recovery of Cr (VI) from Wastewater

The addition of any organic, inorganic, biological, or radiological substance to water that changes its physical and chemical properties is known as water pollution. These pollutants come in contact with water by rapid and unplanned industrial progress, overpopulation, discharge of sewage into water bodies, etc and such water is unfit and very harmful to public health, animals, plants, and aquatic life.

Intergranular Corrosion Analysis of Austenitic Stainless Steels in Molten Nitrate Salt Using Electrochemical Characterization

This study investigates the influence of molten nitrate salt exposure on the intergranular corrosion (IGC) behavior of three grades of austenitic stainless steel (namely, AISI 304, AISI 304H, and AISI 321H). Two electrochemical techniques, double loop electrochemical potentiokinetic reactivation and potentiodynamic polarization methods, are applied after stainless steel is exposed to 600 °C molten nitrate salt, 60% NaNO3, and 40% KNO3 for varying immersion durations. Corrosion morphology is examined using optical microscopy and scanning electron microscopy images to assess susceptibility to IGC. IGC is prompted by the presence of chromium carbides at grain boundaries, which leads to chromium depletion around these carbides. The findings of the experiments reveal distinct IGC behavior among stainless steel grades. For AISI 304, the degree of sensitization (DOS) increases as exposure time progresses. However, AISI 304H and AISI 321H stainless steel exhibit diminishing DOS after 100 and 10 h of exposure, respectively. This trend is attributed to desensitization or the healing effect when stainless steel is exposed to molten salt for a prolonged time. The depletion and recovery of Cr near grain boundaries are confirmed by the inverse relationship to DOS of pitting potential.

Biosorption and desorption of chromium using hybrid microalgae-activated sludge treatment system

This study utilised a mixed culture of Chlorella vulgaris and bacteria from sludge to treat synthetic tannery wastewater (STWW) in modified stirred-tank photobioreactors (MSTPBRs). The MSTPBRs were fabricated locally and operated at irradiance value of 580 µmol/m2s supplied by red light-emitting diodes at 12:12 light–dark cycles and 100 ± 1 rpm continuous stirring. In each case, 50, 100 and 150 mg/L concentrations of STWW were inoculated with mixed culture of microalgae and bacteria in three MSTPBRs, with the control MSTPBR operating at 50 mg/L of STWW. Chromium concentrations were measured using colorimeter whilst Fourier transform infrared spectroscopy (FTIR) indicated possible Cr biosorption. Maximum Cr (VI) and total Cr removal efficiencies of 93 and 94% were achieved, with more than 78% total Cr recovery. Results from FTIR suggested involvement of Chlorella vulgaris in the Cr biosorption. The hybrid microalgae-bacteria system efficiently treated tannery wastewater with considerable Cr removal efficiencies. The potentials of the system in treating tannery wastewater in larger scale may require further investigation.

Adsorption and recovery of Cr(vi) from wastewater by Chitosan–Urushiol composite nanofiber membrane

Abstract Chitosan (CS) is widely used in the treatment of wastewater containing metal ions. However, the poor stability in acidic aqueous solutions severely limits its application in many practical scenarios. In this work, a CS-based composite nanofiber membrane was prepared by electrospinning using urushiol, a natural biomaterial, as the cross-linking agent. The application of the CS-urushiol (CS-U) membrane in the adsorption and recovery of Cr(vi) in wastewater was systematically studied. The CS-U membrane showed great resistance to strongly acidic and oxidative environments, and the adsorption process combined two mechanisms of electrostatic attraction and redox reaction. Due to the nanoscale fibers, porous structure, and strong acid resistance, the CS-U membrane adsorbed Cr(vi) rapidly and efficiently in both batch and continuous modes. Moreover, the adsorption capacity and selectivity of the CS-U membrane for Cr(vi) could be maximized simultaneously by adjusting the solution pH, promoting the recovery of high-purity Cr2O3.

Efek Pre-Roasting Terhadap Parameter Kinetika Leaching Cr dari Limonit

Hydrometallurgical processes such as leaching of limonite ore to extract valuable metals including Ni and Co are often non-selective, including other metals in the leachate product. The leaching behavior of Cr from the chromite mineral contained in limonite ore is of concern due to the high Cr content of the leachate effluent. The pre-roasted process is frequently used to pre-treat limonite to increase the precious metal content. This study aims to determine the leaching behavior of Cr and the effect of pre-roasting on its kinetic parameters. The pre-roasting process was carried out at 280 and 610 oC for 4 hours. Observation of Cr leaching behavior was carried out in the leaching temperature range of 30-90 oC for 0-120 minutes using sulfuric acid solvent. The highest Cr recovery was achieved in pre-roasted ore leaching at 610 oC with leaching operating conditions of 2 M sulfuric acid, solid-liquid ratio of 5 g/50 mL, 200 rpm, for 120 minutes, at a leaching temperature of 90 oC, under these conditions Cr recovery reached 53.16%. The higher the roasting temperature, the lower the activation energy required for the leaching process. Cr leaching from raw and pre-roasted ore is controlled by the diffusion process through the ash layer with activation energies (EA) of 21.41, 18.64, and 14.71 kJ/mol for raw ore, pre-roasted ore 280 oC, and pre-roasted ore 610 oC, respectively. The comparison of kinetics data from several roasting products for atmospheric leaching feeds will provide industry with information to integrated pyro-hydrometallurgical process to increase Cr production from laterite.

A novel method for effective solidifying chromium and preparing crude stainless steel from multi-metallic electroplating sludge

Electroplating sludge (ES) is a globally prevalent hazardous waste that primarily contains Cr, Cu, Ni, and Fe. However, the residual Cr phases within the slag potentially poses an environmental risk in current vitrification. A novel method for effective recovering and solidifying Cr in ES is proposed in this work. ES was desulfurized and subsequently co-treated with ferrosilicon (Fe-Si) and spent carbon anode (SCA) for enhancing the recovery of Cr, Cu, Ni, and Fe to prepare crude stainless steel. Under optimal conditions, the recovery ratios of Cr, Cu, Ni, and Fe reached 96.96%, 99.45%, 99.92%, and 99.20%, respectively, signifying improvements of 21.4%, 0.2%, 1.5%, and 2.8%, respectively, compared with existing research. Meanwhile, the fluoride in SCA yielded CaF2, further progressing to the Si-Ca-F-Na-Al-O phase, with a solidification ratio of 97.87%. The Cr leaching content of the residual Cr-Cu-S phase in the slag remained below 5 mg/L across a pH range of 2–4, demonstrating enhanced stability compared to prior alloy, oxide, and chemically dissolved phases. An innovative approach for solidify Cr by forming matte holds implications for the treatment of Cr-containing solid wastes such as chromium slag, tannery sludge and stainless steel slag.

PSII-25 Use of Energy Dispersive X-Ray Fluorescence for Determination of Indigestible Markers in Digesta Samples

Abstract Titanium dioxide and chromium ethylenediaminetetraacetic acid are commonly used as indigestible markers for determining passage rates of diets to aid in determination of digestibility. However, commonly used methodology involving acid digestions and utilizing inductively coupled plasma spectroscopy and atomic absorption spectroscopy for both Ti and Cr analysis involves hazardous chemicals, destruction of samples, and low sample throughput. The objective of this experiment was to develop and validate an accurate and precise method for measuring both Ti and Cr using energy dispersive X-ray fluorescence (ED-XRF). Energy dispersive X-ray fluorescence is an analytical technique used for analyzing elements in various sample types. The samples are added to the ED-XRF machine and irradiated with X-rays and the intensity of the X-rays emitted (termed fluorescent X-rays) are used for calculation of the concentration of the element. The method for Ti was constructed using fecal samples from cattle consuming three different diet types (finishing diet, dairy lactation diet, and grazing native range pasture). The Cr method was developed for rumen fluid analysis. To determine accuracy and precision of the method, samples were spiked with various amounts of Ti or Cr and measured for their respective compounds with percent recovery and inter- and intra-assay CV calculated thereafter. Additionally, a regression was performed using PROC REG in SAS 9.4 to determine the relationship between grams of Ti added and grams of Ti recovered for each diet type. The average recovery for Ti across all diet types was 100.3%, and the recovery for Cr in rumen fluid was 95.7%. The average inter- and inter-assay CV for Ti, across all diet types, were 9.70 and 2.16%, respectively. For Cr, the average inter- and inter-assay CV were 5.41 and 8.45%, respectively. Across diet type, the regression for grams of Ti added versus grams of Ti recovered indicated the recovery was not altered by the amount added (P ≤ 0.062). The ED-XRF method requires minimal additional chemicals, is cost-effective, and allows for sample preservation as well as a high throughput of samples. Our results indicate utilization of ED-XRF is an accurate and precise method for determination of Ti in feces and Cr in rumen fluid.

Oxygen-rich and moderate/low temperature calcination treatment of chromium containing sludge for high efficient Cr recovery and toxicity reduction

The chromium (Cr) pollution of soil has recently gained a lot of attention for the demand of environmental protection. One of its main resources is from the landfill of the chromium containing sludge (CCS) that produces from reduction–precipitation treatment of the Cr(VI) wastewater. In this work we provide an improved alkaline oxidation calcination (AOC) treatment for CCS, which achieves high Cr recovery efficiency at relatively low calcination temperature and oxygen-rich conditions. The leaching risk of the final residue is much reduced compared to the conventional calcination. It reveals that by using air flow the oxidation efficiency is effectively improved to a value of near to ∼ 90 % at 450 ℃. The thermal analyses of the reaction suggest that Cr (III) in CCS transforms to chromite at the temperature range of 340–450 ℃, which ensure the subsequent oxidation. On the other hand, it reveals that at higher temperature ( 500 ℃) it will produce CaFe oxides which are confirmed to be dissolved in the leachate of the toxicity test. The concentration of Cr (III) increases obviously, which could be associated with the release of Cr(III) that doped into CaFe oxides as solid solution. The transformations of the CCS components during the AOC process are depicted in detail. The method proposed here enables high oxidation efficiency of CCS and meanwhile avoids the environmental risk of final residue.

Effective removal of Cr (VI) from aqueous solution by reinforced sodium alginate/polyethyleneimine/graphene oxide composite aerogels.

A reinforced composite aerogel absorbent was synthesized using a green chemistry method and an environmentally friendly freeze-drying technique. The absorbent consisted of sodium alginate, polyethyleneimine (PEI), and graphene oxide (GO). The ability of the absorbent to remove Cr (VI) ions from aqueous solutions was studied. PEI was a nitrogen source for Cr (VI) removal and a cross-linking agent for GO sheets, while SA was a reinforcing material. The aerogel was investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, texture analysis, Raman spectroscopy, and thermogravimetric analysis (TGA). Batch studies were conducted to investigate the effect of pH and contact time on adsorption. The results indicated that the SA/PEI/GO aerogel had a maximum adsorption capacity of 174.05 mg·g-1 for Cr (VI) at pH 2. The adsorption mechanism was described using the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. The aerogel demonstrated good regeneration ability and satisfactory recovery for Cr (VI) even after five cycles. These findings suggest that the composite aerogel could be a promising adsorbent for efficiently removing Cr (VI) from wastewater.

Effective Cr(VI) reduction and immobilization in chromite ore processing residue (COPR) contaminated soils by ferrous sulfate and digestate: A comparative investigation with typical reducing agents

Chemical reduction combined with microbial stabilization is a green and efficient method for the remediation of hexavalent chromium (Cr(VI)) contaminated soil. In this study, the combination of ferrous sulfate with kitchen waste digestate was applied to reduce and immobilize Cr(VI) in chromite ore processing residue (COPR) contaminated soils, and systematically evaluated the remediation performance of Cr(VI) compared with several typical reducing agents (i.e., ferrous sulfate, zero valent iron, sodium thiosulfate, ferrous sulfide, and calcium polysulfide). The results showed that the combination of ferrous sulfate and digestate had superior advantages of a lower dosage of reducing agent and a long-term remediation effect compared to other single chemical reductants. Under an Fe(II):Cr(VI) molar ratio of 3:1% and 4% digestate (wt), the content of Cr(VI) in the soil decreased to 5.07 mg/kg after 60 days of remediation. Meanwhile, the leaching concentrations of Cr(VI) were below detection limit, which can meet the hazardous waste toxicity leaching standard. The risk level of Cr pollution was decreased from very high risk to low risk. The X-ray photoelectron spectroscopy (XPS) results further demonstrated that the combined treatments were beneficial to Cr(VI) reduction and stabilization. The abundance of bacteria with Cr(VI) reducing ability was higher than other treatments. Moreover, the high abundance of carbon and nitrogen metabolism in the combined treatments demonstrated that the addition of digestate was beneficial to the recovery and flourishing of Cr(VI)-reducing related microorganisms in COPR contaminated soils. This work provided an alternative way on Cr(VI) remediation in COPR contaminated soils.

Determination of mass-dependent chromium isotopic compositions in geological samples by double spike-total evaporation-thermal ionization mass spectrometry (DS-TE-TIMS)

BackgroundChromium isotopes have been used to trace geochemical and cosmochemical processes in the past. However, the presence of multivalent Cr species has made it difficult to isolate Cr from geological samples, particularly for samples with a low Cr mass fraction. ResultsHere, a simple three-step ion exchange chromatography procedure is presented to separate Cr from various sample matrices, ranging from ultramafic to felsic rocks. Throughout each of the column chromatography step, 1 mL of cation exchange resin AG50W-X8 (200–400 mesh) was used as the stationary phase and oxalic acid as a chelating agent, was used in addition to the inorganic acids. This method yielded high recoveries of Cr [93 ± 8% (2SD, N = 7)] regardless of the lithology. The total procedural blank of Cr was <0.5 ng. We also developed a double spike-total evaporation-thermal ionization mass spectrometry (DS-TE-TIMS) technique that significantly reduced sample consumption to ∼20 ng of Cr per each measurement of mass-dependent 53Cr/52Cr. SignificanceThis study achieved a 2SD external precision of 0.02‰ for the analysis of NIST NBS3112a and of 0.01–0.07‰ for the geological samples. This study enabled high-precision Cr isotope analysis in geological samples with various matrix and Cr compositions using relatively small sample volumes.

Enhanced adsorption performance of a Cu/Ni-MXene composite for phosphate recovery and removal of Cr(VI) from aqueous solutions

In the present study, a CuNiO-MX (CNM) hybrid adsorbent that demonstrates an excellent P recovery and removal of Cr(VI) was prepared through liquid self-assembly method. We investigated the effects of different molar ratios of Cu/Ni (Cu0.0083Ni0.00069O-MX, Cu0.05Ni0.025O-MX, Cu0.1Ni0.05O-MX, Cu0.2Ni0.1O-MX, and Cu0.4Ni0.2O-MX) on P and Cr(VI) removal and compared these samples with bare MXene. The adsorption performance of the CNM samples was superior than bare MXene, and the Cu0.1Ni0.05O-MX adsorbent was observed as the most effectual for P and Cr(VI) removal, with a removal rate that was ∼ 163.2 and 18 times higher for P and Cr(VI), respectively, than bare MXene. The maximum adsorption capacity for P and Cr(VI) was 66.3 mg/P-g and 321.2 mg/g, respectively, at an equilibrium time of 2 h. Cu0.1Ni0.05O-MX also exhibited very higher selectivity for both P and Cr(VI), while adsorption isotherm and kinetics analysis exhibited that the uptake of P and Cr(VI) onto Cu0.1Ni0.05O-MX fits well with Langmuir isotherm and pseudo-second-order models, respectively. Cu0.1Ni0.05O-MX demonstrated an excellent resistance to inorganic anions in natural water, and recycling and reusability tests indicated that Cu0.1Ni0.05O-MX maintained a high adsorption performance for P and Cr(VI) after five cycles. The adsorption-mechanisms for P and Cr(VI) using Cu0.1Ni0.05O-MX were also examined by XPS and FT-IR analysis, showing that the –OH groups played a key role in the removal of the two contaminants. Our findings indicate that the Cu0.1Ni0.05O-MX adsorbent holds great promise for the remedy of wastewater having P and Cr(VI).

Environmental hazard reduction and anti-aging enhancement of steel slag powder-asphalt mastic based on TiO2@UiO-67 composites

Steel slag asphalt pavements (SAPs) will deteriorate during the production and service process, bringing heavy metal ions leaching contamination and irregular release of Volatile Organic Compounds (VOCs), which pose great challenges to maintenance and ecological environment. TiO2@UiO-67 composites were synthesized, their basic physical-chemical properties were investigated, and they were applied to SAPs to prepare an eco-friendly steel slag powder-asphalt mastic (ESAM) with multiple effects of anti-aging, heavy metal ions reduction, and VOCs emission inhibition. The rheological behavior of ESAM was explored, and the anti-aging, heavy metal inhibition, and VOCs reduction mechanism was investigated. The results showed that TiO2@UiO-67 composites with excellent properties such as large surface area, high activity and stability, powerful adsorption ability, controlled structure, and specific functional group/targeted adsorption were prepared. Some terminal hydroxyl groups were reacted with reactive radicals to prevent the growth of asphalt chain segments by reducing the aging of asphalt. The binding energy and adsorption between UiO-67 with heavy metal ions and VOCs were simulated by Materials Studio (MS), and the results showed that the recovery of Cr (VI) was up to 57.7% and the reaction proceeded spontaneously. In addition, the conjugated system, the molecular size and the spatial site resistance synergistically reduced Category 1 carcinogens by up to 85.6%, ultimately reducing the total emission concentration of VOCs by 65.4%. It provides theoretical guidance for the application of TiO2@UiO-67 composites in SAPs, and technical feasibility for anti-aging, and pollutant emission reduction strategies for SAPs.

Application of Granulated Nickel-Aluminum-Zirconium Complex Hydroxide in the Flow Method for Recovery of Chromium(VI) Ions.

A colloidal silicate granulated nickel-aluminum-zirconium (CSG-NAZ) was prepared, and the chromium(VI) (Cr(VI)) ions recovery capacity was evaluated using a sodium sulfate solution in a column experiment. The amount adsorbed and breakthrough time were enhanced by decreasing the flow rate (flow rate is in the order of 3.0 > 2.0 > 0.5 mL). The breakthrough curves and model parameters were estimated using the Thomas and Yoon-Nelson models. The obtained data confirmed to fit both the Yoon-Nelson model (0.858-0.906) and the Thomas model (0.813-0.906). Additionally, Cr(VI) ions that adsorbed onto CSG-NAZ could be desorbed using a sodium sulfate solution in a column experiment. The total recovery percentage of Cr(VI) ions was 80.9% after six repetitions of adsorption/desorption. Finally, the obtained results revealed that CSG-NAZ was a candidate adsorbent for the recovery of Cr(VI) ions owing to its applicability toward a continuous system.

Highly efficient Cr (VI) removal from electroplating wastewater by regenerable copper sulfides: Mechanism and magical induction effect for Cr resource recovery

The current sorbents used to remove Cr (VI) from electroplating wastewater are faced with some challenges including the difficulty in separating, regenerating, and safely disposing of adsorbed Cr species. To address these challenges, CuSx/TiO2 was developed to recover Cr (VI) from electroplating wastewater. CuSx/TiO2 had superior performance in removing Cr (VI), with the rate and capacity of approximately 9.36 mg g−1 h−1 and 68.8 mg g−1 at initial pH 4.0, respectively. Additionally, Cu2+ released from CuSx/TiO2 during Cr (VI) removal would come back to its external surface as the Cu(OH)2 precipitate at initial pH 4.0, which helped to prevent the generation of secondary pollution. The Cu(OH)2 precipitate would be decomposed into CuOx after calcination, which would then be transformed back into CuSx by re-sulfuration for regeneration. Hence, CuSx showed a magical induction effect on Cr (VI) recovery, and Cr (VI) from electroplating wastewater might be gradually enriched as Cr2O3 in the sandwich between CuSx and TiO2 through multiple regenerations and removals, which could be considered as a chromium ore resource for industrial applications when the amount of enriched Cr2O3 reached more than 30 wt%. Overall, CuSx/TiO2 showed great potential as a promising sorbent for Cr (VI) removal from electroplating wastewater.

Amino-functionalised chrysin as adsorbent in dispersive micro-solid phase extraction of selected heavy metal ions from stingless bee honey

The study includes the preparation, characterisation, and application of a new adsorbent, 3-aminopropyltriethoxysilane modified chrysin (CHY-APTES), to extract Pb(II), Cr(III), and Cd(II) from stingless bee honey samples using dispersive micro-solid phase extraction (d-µ-SPE) and detected by graphite furnace atomic absorption spectrometer. Characterisation techniques of CHY-APTES including Brunauer-Emmett-Teller surface area analysis, Fourier transform infrared spectroscopy, scanning electron microscopy-energy dispersive x-ray imaging and point of zero charge determination. Several parameters were studied and optimised, such as a desorption time of 15 min, an adsorption time of 3 min, the use of nitric acid solution as the desorption solvent, 120 mg of adsorbent mass, solution pH adjusted to pH 5, and ethanol employed as the dispersive solvent. The results demonstrated good relative recoveries for Pb(II), Cr(III) and Cd(II) in the range of 74.76–116.34 %, 83.59–115.83 % and 89.03–117.66 %, respectively, with good precision at a relative standard deviation≤11.46%. For method sensitivity, the method showed acceptable detection limits (3 S/N) for Pb(II), Cr(III) and Cd(II) extracted from stingless bee honey samples at 43.6, 348.9 and 56.7 µg/kg, respectively. The preconcentration factors calculated for Pb(II), Cr(III), and Cd(II) were 111, 9.5, and 49, respectively. The newly developed CHY-APTES was successfully applied in d-µ-SPE for the first time. It was adequate in terms of analytical performance and simple in preparing stingless bee honey samples via dilution.

Chemical beneficiation of chromite ore to improve the chromium-to-iron ratio for ferrochrome production

Ferrochrome (FeCr), a relatively crude alloy comprised primarily of iron (Fe) and chromium (Cr), is vital for the production of stainless steel. FeCr is produced from chromite ore, the most important source of virgin Cr units. FeCr producers are only paid per mass unit of Cr content in the FeCr, i.e. in US¢/lb contained Cr, according to the current global FeCr markets pricing structure. Consequently, FeCr producers transport a large fraction of their product weight, i.e. the Fe content of the FeCr, without any benefit. The Fe content in the FeCr produced depends on the chromite spinel Cr/Fe ratio. Therefore, the selective removal of Fe from the chromite spinel using different combinations of chromite pre-oxidation, pre-reduction, and sulphuric acid leaching was investigated. The Cr/Fe ratio of the case study ores could be increased from 1.57 up to ∼23.4. However, Cr recovery decreased significantly under experimental conditions to achieve such high Cr/Fe ratios. More desirable Cr/Fe ratios of >2 up to ∼4.28 were achieved while maintaining Cr recoveries of >90%.