Alumina Extraction Research Articles

Characteristics of Bauxite Residue–Limestone Pellets as Feedstock for Fe and Al2O3 Recovery

Experimental research was carried out to produce pellets from bauxite residue for the further extraction of iron and alumina. Bauxite residue and limestone with three different mixture compositions were pelletized experimentally via agglomeration followed by drying and sintering at elevated temperatures. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) were used for the phase and microstructural analysis, respectively. Tumble, abrasion, and breaking load tests were applied to determine the strength of the pellets. For measurement of porosity and surface area, mercury porosimetry and BET surface area methods were applied. It was found that at 1100 °C sintering temperature, all the three sintered pellet compositions have a moderate porosity and low strength, but the reverse result was found when 1200 °C sintering temperature was applied. Moreover, for the pellets sintered at 1150 °C high strength and proper porosities were obtained. In the sintered pellets, iron present in form of brownmillerite (Ca2Fe1.63Al0.36O5), srebrodolskite (Ca2Fe2O5), and fayalite (Fe2SiO4), while alumina present mostly in gehlenite (Ca2Al2SiO7) and little fraction in mayenite (Ca12Al14O33) and brownmillerite phases. The identified phases are the same for of the three pellets, however, with variations in their quantities. Porosity and mechanical properties of pellets are inversely related with both varying sintering temperature and composition. It was found that with more CaCO3 use in pelletizing, higher porosity is obtained. However, with increasing sintering temperature the strength of the pellets increases due to clustering of particles, while porosity decreases.

Extraction of alumina and silica from high-silica bauxite by sintering with sodium carbonate followed by two-step leaching with water and sulfuric acid.

Efficient utilization of high-silica bauxite and minimization of bauxite residue are of great significance for the sustainable development of the alumina industry. In this paper, a novel process is proposed to extract Al2O3 and SiO2 from high-silica bauxite without residue discharge, that is, sintering bauxite with Na2CO3 followed by two-step leaching with water and sulfuric acid. The effects of the sintering parameters on the process were investigated, and the phase transformations during sintering and leaching were revealed by using phase diagram, thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) methods. When the mixture of the high-silica bauxite and Na2CO3 with mole ratio of Na2O/(Al2O3 + SiO2) of 1 was sintered at 950 °C for 30 min, diaspore and kaolinite were primarily converted into Na1.95Al1.95Si0.05O4 and an amorphous phase, respectively. In the water leaching process, Na1.95Al1.95Si0.05O4 was dissolved while the amorphous phase underwent some transformations to form the water leaching residue, resulting in ∼84% of Al2O3 being extracted for alumina production. In the sulfuric acid leaching process, the amorphous phase in the water leaching residue dissolved, resulting in ∼13% of Al2O3 and ∼86% of SiO2 being extracted for the production of polyaluminium ferric sulfate (PAFS) and silica gel, respectively. The silica gel had a high purity, containing more than 88% of SiO2 after drying.

Методологический анализ технологического процесса получения первичного алюминия

This analytical review is aimed at investigating the state of the aluminum industry and approaches to automation of aluminum production. An analysis of the principles of modeling such systems and developing control algorithms is carried out. An important part of the review is devoted to the study of existing publications in the field of modeling and development of control systems for the aluminum production process. Extraction of aluminum by electrolysis remains a complex and multifaceted process, which requires new modeling approaches. The latter represents a promising development direction in this field. This work was carried out as part of the Philosophy of Science educational program.

RELATIONSHIP BETWEEN SOIL ACIDITY AND PRODUCTIVITY OF BANANA (Musa spp.) IN URABÁ, COLOMBIA

Soil acidity plays an important role in the productivity of export bananas as it affects nutrient availability and phytotoxicity depending on soil pH. The objective of this research was to evaluate the relationship between soil pH and banana productivity in Uraba, Colombia. The study was conducted at the Ramiro Jaramillo Sossa experimental station, Banana Research Center (Cenibanano), Urabá, Antioquia. The sampling grid consisted of 110 points. Determination of pH was conducted in situ, and soil samples were processed in the laboratory using two solutions: distilled water and KCl. Significant differences were found between the solutions, aluminum extraction and field sampling. Additionally, the presence of Al3+ was confirmed in the pH range H2 O 5.5. Finally, the pH values were pH KCl pH H2 O pH in-situ. The latter best explained the behavior of bunch weight, indicating that in situ determination of pH better reflects the real conditions of this variable, with a greater relationship with productivity.

Integrated chlorination technology for producing alumina and silica from ash-slag waste of the TPP of Kazakhstan

The paper proposes a technology for the disposal of accumulated ash-slag waste in Kazakhstan using chlorinated ash roasting with further leaching of the cinder with hydrochloric acid. The possibility of preliminary separation of iron (Fe3+) from ash by magnetic separation with the production of a commercial iron-containing product (∼50% Fe) and a non-magnetic fraction with a high content of aluminum is shown.It has been established that the preliminary roasting of the non-magnetic fraction of ash at: 1100°С, the consumption of CaCl2 2 times exceeding its stoichiometric consumption required for the decomposition of mullite, holding for 60 min, and leaching in HCl, leads to an increase in the aluminum content in the solution up to 16.09 g/l. As a result of dehydration of hardly soluble compounds an increase in the degree of extraction of aluminum is caused by a change in the phase composition of ash during roasting. In the obtained cinder the gehlenite and anorthite phases are formed which are well soluble in HCl.The influence of HCl consumption, temperature and duration of the process on the degree of dissolution of the main aluminum compounds - gehlenite and anorthite - has been studied. It has been established that at: S:L = 1:3 ratio, HCl concentration = 30%, temperature 60°С and leaching time of 1 h, a high extraction of silica into a solid commercial product is achieved - 99.8% due to the maximum transfer of impurities to solution. The aluminum content in the solution is 16.09 g/l.

Problems of waste rock formation during mining of Western Donbass coal reserves: state-of-the-art and solutions

Purpose. The research purpose is to analyze and generalize the problems of waste rock accumulation, as well as to determine the directions for their possible solution in order to improve the ecological-economic conditions for mining coal reserves in the Western Donbass. Methods. A comprehensive scientific-methodological approach is used, which consists in studying regional accounts on the state of the environment, data from the register of waste disposal sites in the Dnipropetrovsk Oblast, peculiarities of placement of dumps according to the Google Earth program and collected mine data. To study the feasibility of processing dumps, a SWOT-analysis is used, as well as the analysis of existing technologies for processing the rock mass from waste dumps, based on foreign and domestic experience. Findings. Nine rock dumps have been identified, formed as a result of the functioning of the Western Donbass coal mines, where almost 130 million tons of waste rocks have been accumulated on an area of about 190 hectares. It is noted that the reclamation of disturbed lands as the main means of rock utilization is insufficient. Based on a thorough analysis of the SWOT-analysis results, a strategic direction for processing has been determined – the use of rock mass as a raw material for construction (materials and roads) with accompanying extraction of coal, aluminum and iron. The existing technologies for the processing of waste rocks have been systematized. It has been determined that the largest scaling of waste dump processing in the Western Donbass mines can be achieved with a combination of mechanical-chemical methods, among which gravity and magnetic beneficiation methods, mechanical grinding and chemical leaching are priority. Originality. The mechanisms for handling coal waste from coal mines in the Western Donbass have been determined to solve ecological-economic problems associated with their accumulation. Practical implications. The research results reveal possible ways of solving the problems of waste rock accumulation in the Western Donbass mines, which makes ecological and economic sense.

High-Iron Bauxite Residue (Red Mud) Valorization Using Hydrochemical Conversion of Goethite to Magnetite.

Bauxite residue (BR), also known as red mud, is a byproduct of the alumina production using the Bayer process. This material is not used to make iron or other iron-containing products worldwide, owing to its high content of sodium oxide and other impurities. In this study, we investigated the hydrochemical conversion of goethite (FeOOH) to magnetite (Fe3O4) in high-iron BR from the Friguia alumina refinery (Guinea) by Fe2+ ions in highly concentrated alkaline media. The simultaneous extraction of Al and Na made it possible to obtain a product containing more than 96% Fe3O4. The results show that the magnetization of Al-goethite and Al-hematite accelerates the dissolution of the Al from the iron mineral solid matrix and from the desilication product (DSP). After ferrous sulfate (FeSO4·7H2O) was added directly at an FeO:Fe2O3 molar ratio of 1:1 at 120 °C for 150 min in solution with the 360 g L-1 Na2O concentration, the alumina extraction ratio reached 96.27% for the coarse bauxite residue size fraction (Sands) and 87.06% for fine BR obtained from red mud. The grade of iron (total iron in the form of iron elements) in the residue can be increased to 69.55% for sands and 58.31% for BR. The solid residues obtained after leaching were studied by XRD, XRF, TG-DTA, VSM, Mössbauer spectroscopy, and SEM to evaluate the conversion and leaching mechanisms, as well as the recovery ratio of Al from various minerals. The iron-rich residues can be used in the steel industry or as a pigment.

Experimental research on the properties of foamed mixture lightweight soil with red mud

Red mud (RM) is a kind of alkaline waste produced by the extraction of alumina from bauxite. According to statistics, approximately 1.5 billion tons of RM are produced worldwide annually. The existing storage methods of RM not only occupy a large number of land resources but also damage to environment owing to the presence of highly alkaline and trace heavy metal elements. This study converted wasted RM into foamed mixture lightweight soil (FMLS), a type of eco-friendly material primarily made of foam and cement. Investigations were done into the flowability, unconfined compressive strength (UCS), durability, and microstructure of FMLS with RM (FMLSR). 10 %, 15 %, 20 %, 25 %, and 30 % substitution percentages (by weight) of RM for cement were taken into consideration. The results show that the compressive strength of FMLSR was greatest when the RM replacement percentage was 20 %, and the water stability coefficient of FMLSR was greater than 0.7 when the RM replacement percentage was less than 25 %. Although the FMLSR cured for 28d generated more C-S-H gels and had a better microstructure when the replacement percentage of RM was 20 %, the UCS was still lower than that of FMLS without RM due to the relatively low Ca/Si ratio of the generated C-S-H gels. The utilization of RM not only consumes large amounts of waste and reduces environmental pollution but also frees up many land resources and reduces carbon emissions.

Preparation of monodisperse silica powder from acid residue after extracting alumina from coal gangue

AbstractA new method for preparing monodisperse silica powder was introduced in this paper. Monodisperse silica powder was synthesized by sol–gel method using sodium silicate prepared from acid residue after alumina extraction from coal gangue leached by NaOH. The dissolution rate of SiO2 was determined according to the potassium fluosilicate volumetric method (GB/T 27974‐2011). The SiO2 dissolution rate reaching 92.74% when dissolution temperature calcined at 90°C for 90 min, the liquid–solid ratio was 8 ml/g, and the concentration of NaOH solution was 30%. The maximum specific surface area of silicon powder reaching 519m2/g when the concentration of sodium silicate was 0.6 mol/l, ethyl acetate concentration was 8%, anhydrous ethanol concentration was 5%, and the reaction time was 90 min. X‐ray fluorescence (XRF), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) showed that the content of SiO2 in the powder was 99.28%, the particle size was between 30 ~ 300 nm, and more than 90% of the particle size was below 100 nm.

Reduction of Emissions of Resinous Substances in Extraction of Aluminum by Electrolysis

Reduction of Emissions of Resinous Substances in Extraction of Aluminum by Electrolysis

A new approach of aluminum extraction from drinking water treatment sludge using ammonium sulfate roasting process

The drinking water treatment based on the coagulation-flocculation process using aluminum sulfate is widely used the whole word. As the effect of this activity, the huge quantities of the drinking water treatment sludge continue to be an environmental issue and needs to be valorized. The purpose of the present work is to investigate the valorization pathway of this sludge by extracting aluminum using ammonium sulfate roasting and hot water leaching at 80 °C as an alternative method to acid leaching which is energetic and cause corrosion problems. Several techniques were used, i.e., Thermogravimetric/Differential thermal (TGA/DTA) analysis, X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM), and inductively coupled plasma - optical emission spectrometry (ICP-OES) to approach the reaction mechanism between sludge and ammonium sulfate. This chemical additive promoted the conversion of aluminum and calcium from the primary phases of the sludge, such as calcite (CaCO3), nacrite (Al2Si2O5(OH)4), and muscovite (KAl2(AlSi3)O10(OH)2)to form soluble metal sulfates in a temperature range of 400 °C to 600 °C. The parameters affecting the extraction, such as roasting temperature, mass ratio of ammonium sulfate to sludge, and roasting time were studied. A recovery of 74 % was obtained for aluminum under the optimum roasting conditions. The experimental results showed also a good chemical affinity between ammonium sulfate and other elements present in the sludge, such as calcium, magnesium, and manganese. The extraction efficiency of these elements was 88 %, 91 %, and 77 %, respectively. The characterization of the leaching residue showed the presence of silicon at high content (35.8 %) and low contents of calcium (0.64 %), magnesium (0.16 %), aluminum (2.75 %), and manganese (0.05 %), which confirm the efficiency of the developed process.

Effect of Different Activators on Properties of Slag-Gold Tailings-Red Mud Ternary Composite

Red mud is a kind of solid waste produced in the process of aluminum extraction. Traditional methods of red mud treatment, such as open-pit accumulation and chemical recovery, are costly and environmentally hazardous. Gold tailings are industrial by-products produced in the process of gold mining and refining. In this study, NaOH, KOH, and Na2SiO3 were used as activators, and their effects on the properties of ternary cementitious composite containing blast furnace’s slag, gold tailings, and red mud were studied with the intention of preparing a new cementitious material that is an efficient recovery and utilization of solid waste. The macroscopic mechanical properties and hydration of the ternary cementation material were studied by means of compressive strength, XRD, FT-IR, and TG/DTG. The compressive strength testing showed that the maximum strength at 28 d was 43.5 MPa. The hydration products in the ternary cementitious system were studied by SEM and EDS, and it has been demonstrated that the strength of this cement was due to the formation of Aft (AFt, also known as Ettringite, has the chemical formula 3CaO·Al2O3·3CaSO4·32H2O. It is one of the important hydration products of cement-based cementitious materials, which can not only provide early strength for cement, but also compensate for early shrinkage of concrete.) and C-A-S-H gels. Samples activated by Na2SiO3 presented a most compact microstructure and the best macroscopic mechanical properties than the samples free of activator. The toxicity tests results showed that the content of heavy metal ions liberated by the cement’s leaching met the standard requirements, proving that the slag-gold tailings-red mud ternary composite was environmentally friendly.

(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award) Electrochemically Grown Highly Textured Thick Ceramic Oxide Films for Energy Storage: A New Manufacturing Paradigm for Cathode Materials

Electrochemical synthesis of materials has contributed to significant breakthroughs in materials processing by replacing high temperature, cost and energy intensive pyrometallurgical processes. Noteworthy examples include aluminum extraction by Hall–Heroult process, electrowinning of copper, titanium extraction through the Kroll process, electrolytic production of steel, and electrochemical synthesis of cement. Increasing the energy and power density of alkali ion intercalated transition metal oxide cathodes which power electric cars and portable electronics, has been a growing topic of global techno-economic interest. Our work demonstrates a direct electrodeposition of thick ternary ceramic oxide films as an alternate scalable manufacturing technique for fabrication of binder-and-additive free cathode materials for secondary battery. Employing an intermediate temperature (200-400°C) molten hydroxide-based electrodeposition method, a general electrochemical growth strategy for multiple Li and Na ion cathode chemistries is demonstrated for the first time including NaCoO2, NaMnO2, LiCoO2, Li2MnO3, LiMnO2, LiMn2O4, (A. Patra, P.V. Braun et. al, PNAS, 2021) in a thick (> 50 µm) thick film form factor. In-plane and through-plane texture can be electrochemically architectured in LiCoO2 and NaCoO2 films across multiple textures: <003>||ND (Li/Na ion blocking sites parallel to the normal direction), <101>||ND, <104>||ND, <110>||ND (fast lithium ion conducting sites parallel to the normal direction). An accurate control of crystallization dynamics leads to highly anisotropic, grain boundary engineered structure with low tortuosity and fastest electron and Li ion conducting pathways (<110>||ND) oriented normal to the current collector. The highly textured (<110>||ND), dense (>95%) electroplated cathodes can perform even at ultrahigh thickness of ~ 200 µm (areal capacity of ~13.6 mAh/cm2) in comparison to 40-60 µm for conventional slurry cast cathodes (areal capacity of ~3-4 mAh/cm2 with a porosity of ~10-20%), a fivefold increase in areal capacity and volumetric energy density (A. Patra, P.V. Braun et. al, to be submitted). In order to enable a high voltage (> 4.5 V vs. Li) cathode design, a functionally graded architecture is also demonstrated with a core capable of providing high-capacity and rate capability (LCO <110>||ND); and multiple capping layers (LCO <003>||ND and Li2MnO3) to suppress harmful side reactions occurring at voltages beyond the normal operation range (beyond 4.2 V vs. Li). Our work paves the way towards an electrosynthesis platform for functional oxides with the ability to generate micron scale ordering with controllable in-and-through-plane orientation in thick ceramic oxide films important for electrochemical energy storage.

Solar driven photocatalytic dye degradation through the novel Ti2C– ZnCo2O4MXenes nanocomposite

Two-dimensional (2D) zinc cobalt oxide (ZnCo2O4) has considerable promise material for efficient dye photocatalytic degradation. A novel family of two-dimensional anisotropic carbides and nitrides from early transition metals (MXenes) is particularly fascinating among 2D materials, such as graphene, due to their potential uses in electronics, medicine, and photo-catalysis. The extended Ti2C phases were created by synthesizing them from their parent Ti2AlC MAX phases under the same circumstances as the traditional acidic aluminum extraction procedure. However, due to its limited specific surface area and high carrier recombination rate, photo-catalytic performance is usually inadequate. Preparation, morpho-structural characterization, band gap measurement, and congo red photo-degradation potential of Ti2C MXene and three nano-composites made up of MXene enhanced by ZnCo2O4 are presented in this study. SEM images revealed hill like agglomerated rough microstructure with round shape many particles morphology. The experimentally obtained band gaps using Tauc's approach are in the 2.60–2.84 eV range. In recent years, the approach of photo-catalytic breakdown of contaminants employing semiconductor photo-catalysts with UV–visible light has grown in importance. The addition of ZnCo2O4 boosted the establishment of strong interfacial coupling between Ti2C and ZnCo2O4, shortening the route of carrier transfer and promoting the direct transfer of photo-generated electrons from Ti2C's valence band to ZnCo2O4.The specific surface area of composites increased significantly at the same time, which was beneficial for improving the UV-absorption capability of Ti2C composites. This research proposes a practical design method for increasing the degrading performance of 2D photo-catalysts, which may serve as a technical suggestion for the modification design of additional photo-catalysts. The MXene based nano-composites revealed high activity in the congo-red photo-degradation reaction (56%–78% of degraded congo-red after 270 min). Ti2C(97%)/ZnCo2O4(3%) composite showed an enhanced efficiency for degradation of congo-red.

Natural rubber composites with antioxidant‐loaded activated calcium silicate for improved thermo‐oxidative aging resistance

AbstractGreen and low‐cost methods are required as alternatives to conventional approaches for impeding the thermo‐oxidative degradation of natural rubber (NR). Herein, to improve the dispersibility of N‐1,3‐dimethylbutyl‐N′‐phenyl‐p‐phenylenediamine (antioxidant 4020) and simplify the loading procedure, antioxidant 4020 was precipitated from acetone using activated calcium silicate (ACS), a byproduct of alumina extraction from fly ash, as a carrier. In the obtained antioxidant 4020‐loaded ACS (ACS‐4020) particles, which had a loading of 7.8%, the antioxidant was physisorbed on the surface of ACS with a uniform distribution. In composites with NR, ACS‐4020 was uniformly dispersed in the NR matrix via chemisorption. ACS‐4020/NR exhibited a faster vulcanization speed, better static mechanical properties, and greater thermal stability than the composite in which antioxidant 4020 was directly integrated (ACS/4020/NR). Changes in the tensile strength, elongation at break, hardness, and thermo‐oxidative aging degree of the composites at different aging times and temperatures showed that ACS‐4020/NR had enhanced resistance to thermo‐oxidative aging. Furthermore, the nitrogen‐containing compounds in ACS‐4020/NR were more stable and performed better against thermo‐oxidative aging. These findings can act as guidelines for the preparation of NR composites with superior thermo‐oxidative aging resistance.

Relationship between thermal dehydroxylation and aluminium extraction from a low-grade kaolinite: Role of clay chemistry and crystallinity

The presented research investigates the impact of clay crystallinity and iron oxide content on thermal dehydroxylation of kaolinite and thus the impact on aluminium dissolution. Two clay samples with different crystallinity and purity levels (designated low-grade for the impurity rich and disordered kaolin, and high grade for the highly crystalline and relatively pure kaolin) underwent thermal treatment from ambient temperature to 850 °C in 50 °C increments, followed by acid digestion to recover aluminium. Infrared spectroscopy and X-ray diffraction were used to characterise the clays after thermal treatment and following acid digestion to gain insights into the chemistry of the process. Lower temperatures were required to achieve complete thermal dehydroxylation for the low-grade kaolin at 450 °C, in comparison to high-grade kaolin, which was complete at 650 °C. Solid-state 27Al Nuclear magnetic resonance (NMR) highlighted the emergence of Al(IV) at 600 °C and Al(V) at 650 °C, the latter of which corresponded to the complete thermal dehydroxylation of the kaolinite and was the main aluminium species responsible for aluminium dissolution. The iron oxide phases present within the low-grade kaolin resulted in phase transformation to insoluble aluminium spinels at lower temperatures (750 °C), which caused a reduction in the acid solubility of aluminium and iron. However, there were benefits associated with aluminium recovery from the low-grade kaolin, namely, less energy being required to achieve complete thermal dehydroxylation for aluminium dissolution. This finding holds significance for the utilisation of low-grade kaolin by industry, such as for production of new commodities such as high purity alumina.

Utilization of hazardous red mud in silicone rubber/MWCNT nanocomposites for high performance electromagnetic interference shielding

With burgeoning technological advancement in telecommunication and high frequency electronics, its repercussion as electromagnetic pollution is alarmingly high. Hence, much effort has been made to supress this undesired phenomenon using efficient electromagnetic interference (EMI) shielding materials. Red mud, a hazardous by-product of alumina extraction is rich in oxides of iron, aluminium & titanium with ca. 30–60% of hematite, a magnetic lossy material that could be suitable for enhancing microwave absorption and EMI shielding performance of polymer nanocomposites. The impetus for this work was to utilize red mud as magnetically lossy filler in silicone rubber (SR)/multi-wall carbon nanotube (MWCNT) nanocomposites to function as efficient EMI shields with superior microwave absorption. Herein, taking the advantage of conductive percolated network of MWCNT in SR, red mud was incorporated with varying concentration of 5–20 wt% & compression moulded to form flexible sheets. These nanocomposite sheets exhibited a maximum electrical conductivity of 24 S/cm with superior EMI shielding effectiveness value of −83.4 dB in the X band (8.2–12.4 GHz) region making it a suitable candidate for commercial shielding applications. Moreover, sustainable use of a hazardous industrial waste to suppress EMI, which is yet another challenging invisible pollutant, is the key highlight of this work.

EXTRACTION OF Al3+, Pb2+, Cd2+ AND Sr2+ IONS WITH A PHOSPHORUS-CONTAINING PRODUCT FROM RICE FLOUR

Materials of natural origin can serve as raw materials for the production of environmentally friendly inexpensive polyfunctional materials with a wide range of applications. Agricultural waste from rice production (rice husks, straw and flour) can serve as a source of such substances. In this work, the process and conditions for the extraction of aluminum, lead, strontium and cadmium ions from aqueous solutions by an organophosphorus product (derivative of inositol hexaphosphoric, phytic acid) obtained from rice flour production waste are studied. Phytic acid and its derivatives are highly effective ligands capable of chelating metal cations, which allows them to be considered as a natural material suitable for removing heavy metal ions from aqueous solutions. The degree of extraction of aluminum ions reaches 97%, lead and strontium – 89%, and cadmium – 93%. It is shown that the absorption decreases in the series Cr3+ &gt; Al3+ &gt; Bi3+ (from 13.0 mg/g to 4.9 mg/g) and Cd2+ &gt; Pb2+ &gt; Sr2+ (from 8.9 mg/g to 7.5 mg/g). These studies allow us to offer a fundamental possibility of using a natural phosphorus-containing compound as an environmentally friendly sorbent.

A novel process for one-step preparing potassium-containing fertilizer using red mud or CFA synergistic extraction of alumina

Red mud and coal fly ash (CFA) are bulk aluminum-containing solid waste in the industrial production process, posing a great threat to the environment and ecological security. The present paper proposes a novel method for one-step producing potassium-containing fertilizer synergistically extracting Al2O3 by KOH hydrothermally treating red mud or CFA. In this paper, the dissolving ratio of Al2O3 in the K2O-Al2O3-H2O ternary system and the extraction of Al2O3 from red mud or CFA after hydrothermal treatment with KOH were investigated. The phase structure transformation of leaching residue obtained under various conditions was analyzed by X-ray diffraction and scanning electron microscopy, and the fertilization efficiency of the products was verified by potting experiments. The results show that the dissolving ratio of Al2O3 can reach the highest value of 85.04% at 120 °C with the K2O mass fraction of 24.90% in the ternary system. When red mud or CFA was hydrothermally leached with 240 g/L K2O at 240 ℃, the Al2O3 extraction rates of 25.50% and 31.42% could be separately obtained, and the leachate could be reused. The main phases of the leaching residue were kaliophilite, illite, and megakalsilite, and the content of K2O was 7.83% and 26.89%, which can be applied as potassium-containing fertilizer to improve soil fertility and effectively promote the growth of pakchoi. The process improves the comprehensive utilization of red mud and CFA without secondary pollution, reduces the negative impact on the environment, and opens up a new way to apply bulk solid waste in the agricultural field.

Economic and fast electro-flotation extraction of heavy metals from wastewater

ABSTRACT Fast electroflotation extraction of heavy metals from wastewater is described. The results of experimental investigations of the extraction of iron, aluminium and chromium hydroxides from aqueous solutions in the presence of surfactants of various natures and ions of calcium by electroflotation are presented. It was found that the presence of Ca2+ in the solution at a concentration of 0.5 g/L reduced the degree of electroflotation extraction of Al(OH)3, Fe(OH)3, Cr(OH)3 regardless of the nature of the electrolyte. The addition of surfactants in the system in the presence of Ca2+ increased the amount of extraction of the dispersed phase. The greatest effect is achieved with the help of anionic surfactant sodium dodecyl sulphate, while the degree of extraction reached 98%. The high efficiency of the process of electroflotation extraction of the dispersed phase was due to the hydrophobization of the particle surface owing to the adsorption of surfactants on the surface of hydroxides. The recent method is useful to treat wastewater contaminated with aluminium, iron and chromium metal ions. The reason is that this method is very fast working within 20 min; Moreover, pH 7.0 working made this method ideal for utilisation in natural water treatment economically.