Acid-activated Kaolin Research Articles

Phosphate removal by acid-activated and chitosan-composite clayey soils

Phosphate is a vital nutrient for aquatic organism growth, but excessive levels can lead to eutrophication, with detrimental effects on receiving water bodies. Adsorption using clay soils can address phosphate release and has gained attention owing to its cost-efficiency and environmental friendliness. To overcome the limited phosphate adsorption capacity of clay soils due to surface charges, the combined effects of acid activation and composite formation with chitosan were investigated. Kaolin and bentonite were selected for acid activation, while chitosan varieties with low, medium, and high molecular weights were chosen for composite formation. Batch tests were individually conducted on acid-activated clay soils and composites of acid-activated clay soils with chitosan over 24 h, varying the initial phosphate concentrations. For acid activation, clay soils were treated with 6N hydrochloric acid, whereas composite formation was achieved via combination with each chitosan variant. Acid-activated kaolin and bentonite individually exhibited phosphate removal efficiencies ranging 99.8–79.8% and 97.1–47.2%, respectively. Among their respective composites, acid-activated kaolin with medium-molecular-weight chitosan and acid-activated bentonite with low-molecular-weight chitosan had the highest phosphate removal efficiencies. Therefore, in contrast to kaolin, acid activation or composite formation of acid-activated bentonite with chitosan can improve its phosphate removal efficiency.

Eco-efficient treatment of hazardous bauxite liquid-residue using acid-activated clays

The alumina industry requires a material capable of reducing the high levels of iron and alkalinity in bauxite liquid-residue in an eco-efficient manner while producing fewer by-products. This study looked at the efficacy of acid-activated kaolin (AAK) and acid-activated bentonite (AAB) in reducing the high pH value and iron content of bauxite liquid-residue in a single treatment step. The bauxite residue, AAB, and AAK were characterised using XRD, XRF, and FTIR techniques. A batch adsorption study with varying contact times and adsorbent types was conducted, and the results were analysed using adsorption kinetics and isotherm studies. The results showed that AAK and AAB could effectively remove 88% to 94% of the total iron in the bauxite liquid-residue. Similarly, the initial pH value of the bauxite liquid-residue (9.93 ± 0.13) was reduced by about 3.32% with AAK and 4.53% with AAB, respectively. Thus, batch adsorption studies revealed that adsorption capacity was strongly pH dependent, and the type of adsorbent had an effect on the reduction of iron and pH value in the bauxite liquid-residue. The AAB was found to be more effective than AAK in lowering the high pH value and iron content of the bauxite liquid-residue.

Cobalt loaded organic acid modified kaolin clay for the enhanced catalytic activity of hydrogen release via hydrolysis of sodium borohydride

Inorganic acids such as hydrochloric acid (HCl), nitric acid (HNO3) and sulphuric acid (H2SO4) are generally used in the acid modification of clays. Here, CoB catalyst was synthesized on the acetic acid-activated kaolin support material (CH3COOH -kaolin- CoB) with an alternative approach. This prepared catalyst, firstly, was used to catalyze the hydrolysis of NaBH4 (NaBH4-HR). The structure of the raw kaolin, kaolin-CH3COOH, and CH3COOH-kaolin-CoB samples were characterized by X-ray diffraction spectroscopy (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM), and nitrogen adsorption. At the same time, this catalyst performance was examined by Co loading, NaBH4 concentration, NaOH concentration, temperature and reusability parameters. The end times of this hydrolysis reaction using raw kaolin-CoB and CH3COOH-kaolin-CoB were found to be approximately 140 and 245 min, respectively. The maximum hydrogen generation rates (HGRs) obtained at temperatures 30 °C and 50 °C were 1533 and 3400 mL/min/gcatalyst, respectively. At the same time, the activation energy was found to be 49.41 kJ/mol.

Adsorption of heavy metal from industrial wastewater onto low-cost Malaysian kaolin clay-based adsorbent.

Adsorption capacity and percentage removal efficiency of Cu(II) and Ni(II) ions were studied and compared between raw kaolinite and acid-activated kaolinite. Acid-activated kaolin was prepared by refluxing raw kaolinite with concentrated sulphuric acid followed by calcination to enhance its surface properties and adsorption ability. Both raw and acid-activated kaolinite samples were characterized by Fourier transform infrared spectroscopy, energy dispersive X-ray, scanning electron micrograph and zeta potential analysis. Upon acid treatment, acid-activated kaolinite was discovered to have altered chemical composition and larger BET surface area as compared with raw kaolinite. The batch adsorption studies on aqueous solution were performed under different factors such as contact time, pH condition, adsorbent dosage, initial metal ion concentration and temperature. The optimum condition was selected for each factor including a contact time of 60min, pH of 7.0, adsorbent dosage of 0.1g, initial metal ion concentration of 100mg/L and temperature of 25°C. Then, the adsorption studies on wastewater samples were carried out at the selected optimum conditions. Acid-activated kaolinite always had better adsorption capacity and percentage removal efficiency than raw kaolinite due to the increasing amount of negative charges on the adsorbent surface and the number of metal ion binding sites upon acid treatment. The adsorption kinetic obtained was well described by the pseudo-second-order model, whereas the adsorption isotherms obtained were well described by either the Freundlich or the Langmuir adsorption model. The results showed that acid-activated kaolinite adsorbent is a better option as a favourable and feasible commercial low-cost adsorbent for wastewater treatment.

Kinetics of African pear seed oil (APO) methanolysis catalyzed by phosphoric acid-activated kaolin clay

Kinetics and mechanism of heterogeneous transesterification reaction of African pear seed oil (APO) catalyzed by phosphoric acid-activated kaolin clay to produce biodiesel were investigated. Heterogeneous catalyst synthesized by activating clay with phosphoric acid was used to examine the effect of time, temperature, methanol/oil molar ratio, catalyst concentration and agitation speed on the production of biodiesel. The kinetics was studied using two elementary reaction mechanisms: Eley–Rideal (ER) and Langmuir–Hinshelwood–Hougen–Watson (LHHW). The results obtained showed that the clay belongs to kaolinite group and acid-activated clay catalyst, AAC was able to convert APO to standard biodiesel with the variation of catalyst concentration, temperature methanol, speed and reaction time having significant effect in the production. About 78–80% biodiesel production was obtained with 10:1 methanol/oil molar ratio, 3 wt% AAC catalyst concentration, time 3 h, speed 300 rpm and at 60 °C temperature. The kinetics result revealed that the LHHW is the most reliable representation of the experimental data using acid-activated clay catalyst with surface reaction between adsorbed triglyceride and adsorbed methanol as rate determining step (RDS). The activation energy for the forward reaction was determined to be 10.08 kJ/mol. Hence, the production of biodiesel from non edible oil APO with cheap and available heterogeneous catalyst (AAC) is achievable.

Synthesis and characterization of hierarchical nanoporous HY zeolites from acid-activated kaolin

Hierarchical nanoporous HY zeolites were synthesized from acid-activated kaolin. The hierarchical factor (HF) was maximized by varying the aging and crystallization time. This was achieved by maximizing the external surface area without greatly reducing the micropore volume. The resulting products were characterized using X-ray diffraction (XRD), X-ray fluorescence, N2 adsorption, and NH3 temperature-programmed desorption. The nanoporous HY zeolite with the highest HF was obtained by aging for 48 h and a crystallization time of 24 h. The acidity and crystallinity varied depending on the operating parameters. Incorporation of an appropriate amount of NaCl was also vital in maximizing the HF, crystallinity, and acidity. The sample crystallinities were determined by comparing their XRD peak intensities with those of a conventional Y zeolite. The results show that optimizing this process could lead to a widely acceptable commercial route for HY zeolite production.

Magnetic modification of acid-activated kaolin: Synthesis, characterization, and adsorptive properties

Maghemite (γ-Fe2O3) nanoparticles were synthesized onto the surface of acid-activated kaolin (AAK), prepared by calcination and acid activation of a coal bearing kaolin, by immobilizing an Fe–urea complex ([Fe(NH2CONH2)6](NO3)3) and subsequent calcination. The obtained samples were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetic measurements, and transmission electron microscopy (TEM). The results confirm the formation of ferromagnetic γ-Fe2O3 nanoparticles, approximately 18nm in size, onto the AAK surface. The obtained γ-Fe2O3/AAK nanocomposite has a high Brunauer–Emmett–Teller (BET) surface area of 99.4m2/g and possesses ferromagnetic characteristics with a maximum magnetization of 26.5emu/g. The adsorption ability of γ-Fe2O3/AAK nanocomposite was investigated using methylene blue (MB) as a typical pollutant. Owing to its high surface area, the γ-Fe2O3/AAK nanocomposite showed higher removal efficiency for MB than for parent kaolin, with a maximum adsorption capacity of 50.2mg/g. The adsorption kinetics of MB fit well with the pseudo-second-order kinetic model, and the equilibrium data can be well described by the Langmuir adsorption model.

Conversion of waste polypropylene to liquid fuel using acid-activated kaolin.

Waste polypropylene was subjected to thermal degradation in the presence of kaolin and acid-treated kaolin, with different catalyst-to-plastics ratios, in a semi-batch reactor at a temperature range of 400-550°C to obtain optimized process conditions for the production of liquid fuels. The effects of process temperature, catalyst and feed composition on yield and quality of the oil were determined. For a thermal decomposition reaction at up to 450°C, the major product is volatile oil; and the major products at a higher temperature (475-550°C) are either viscous liquid or wax. The highest yield of condensed fraction in the thermal reaction is 82.85% by weight at 500°C. Use of kaolin and acid-treated kaolin as a catalyst decreased the reaction time and increased the yield of liquid fraction. The major product of catalysed degradation at all temperatures is highly volatile liquid oil. The maximum oil yield using kaolin and acid-treated kaolin is 87.5% and 92%, respectively, at 500°C. The oil obtained was characterized using GC-MS for its composition and different fuel properties by IS methods.

Adsorption of uranium (VI) from aqueous solution on calcined and acid-activated kaolin

Kaolin was modified by calcination followed by acid-activation. This type of modification strongly increased the adsorption of uranium (VI) on kaolin. The equilibrium data agreed very well with the Langmuir model. Kinetic studies showed that the adsorption followed the pseudo-second-order model. Thermodynamic parameters showed the endothermic heat of adsorption and the feasibility of the process.

Small bin trials to determine the effectiveness of acid-activated kaolin against four species of beetles infesting paddy under tropical storage conditions

Control of populations of Rhyzopertha dominica, Sitophilus oryzae, Tribolium castaneum and Oryzaephilus surinamensis infesting paddy treated with acid-activated kaolin (AAK) at 0.75% w/w or with pirimiphos-methyl (PM) diluted with AAK to give 2 mg PM/kg paddy was compared with that in untreated paddy or paddy admixed with a 2% PM dust formulation on talc at 8 mg a.i./kg. Grain was stored in 45 kg lots in fibreboard drums for 250 days and subjected to periodic infestation with the beetles. All three treatments controlled adult populations of the insects up to 200 days post-treatment, but R. dominica populations started to increase at 250 days in the treatment using 2% PM dust, and this treatment gave progressively lower mortality of R. dominica and less suppression of progeny development in 7 day bioassays using samples taken through the trial than the other treatments. Mean % breakdown of PM formulated on AAK was about twice that on untreated kaolin in accelerated storage tests, and PM residues declined at a faster rate in paddy treated with the mixed dust formulations of AAK and PM than in paddy treated with the 2% PM dust formulation. The deactivator diethylene glycol could be incorporated at up to 10% w/w in AAK with negligible effect on the insecticidal activity of the dust to R. dominica.

Laboratory evaluation of acid-activated kaolin to protect stored paddy against infestation by stored product insects

The toxicity of acid-activated kaolin to adult populations of Sitophilus oryzae, S. zeamais, Tribolium castaneum, Cryptolestes pusillus, Oryzaephilus surinamensis and Rhyzopertha dominica was assessed by admixing the material with paddy and determining mortality at 72 hr. C. pusillus and O. surinamensis were highly susceptible to the desiccant effect, while T. castaneum and the Sitophilus spp were relatively tolerant; the susceptibility of all species to the material decreased as paddy moisture content was increased from 7.2 to 19.2%. A dose of approx. 5 g/kg considerably reduced F 1 progeny production of all the above species and of Sitotroga cerealella. Subsequent heat treatment of acid-activated kaolin had no significant effect on either its oil adsorption capacity or its toxicity to the species tested.