Xuewei Li

Synthesizing slow-release fertilizers via mechanochemical processing for potentially recycling the waste ferrous sulfate from titanium dioxide production

The goal of this study is aimed to develop a novel process to recycle the ferrous sulfate, the by-product of titanium dioxide industry. Zinc sulfate was added in the process of milling ferrous sulfate with calcium carbonate (CaCO3). The sulfates were transformed into carbonates to serve as slow-release fertilizers by co-grinding the starting materials of FeSO4·7H2O, ZnSO4·7H2O, and CaCO3 with small amounts of water in a planetary ball mill. The prepared samples were characterized by X-ray diffraction (XRD) analysis and quantitative measurements of the soluble ratios in water and 2% citric acid solution. It was found that Fe and Zn ions as sulfates were successfully combined with CaCO3 to form the corresponding Fe and Zn carbonates respectively. After milling, the release ratios of Fe and Zn nutrients in distilled water could be controlled at 0.1% and 0.7% respectively. Meanwhile, the release ratios of them in 2% citric acid solution were almost 98% and 100%. Milling speed was the critical parameter to facilitate the transformation reaction. The proposed process, as an easy and economical route, exhibits evident advantages, namely allowing the use of widely available and low-cost CaCO3 as well as industrial wastes of heavy metal sulfates as starting samples to prepare applicable products.

Precursor preparation of Zn–Al layered double hydroxide by ball milling for enhancing adsorption and photocatalytic decoloration of methyl orange

An amorphous photocatalyst was prepared via simple dry milling of Zn basic carbonate (Zn4CO3(OH)6·H2O) and Al hydroxide (Al(OH)3) as a precursor of Zn–Al layered double hydroxide (LDH) and the precursor was agitated in water to simply synthesize the Zn–Al LDH for comparison. The adsorption and photocatalytic activity of the Zn–Al LDH and the precursor were studied via the removal of methyl orange (MO) and decoloration of MO under ultraviolet light irradiation in aqueous solution, respectively. The precursor exhibits much higher decoloration efficiency towards MO than the Zn–Al LDH product because of the synergistic effect of the intercalation reaction and its photocatalytic activity. The amorphous precursor could easily incorporate MO molecules to form MO intercalated LDH, allowing easy access of the organic pollutant to the photocatalyst sample, resulting in an obvious improvement in photocatalytic performance. The novel idea to use the precursor sample instead of the synthesized final product may be applied in other fields to increase the required performances.

Simultaneous synthesis of ettringite and absorbate incorporation by aqueous agitation of a mechanochemically prepared precursor

Co-grinding of calcium hydroxide, aluminum hydroxide and gypsum was performed to prepare an activated precursor for synthesizing ettringite (simple formula 3CaO·Al2O3·3CaSO4·32H2O). Agitation of the precursor in an aqueous solution with a target absorbate, even at room temperature, allowed not only the synthesis of ettringite, but also absorbate incorporation at stoichiometric amounts accompanying the synthesis reaction. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric differential thermal analyses (TG-DSC) were conducted to characterize the precursors and synthesized products. Potassium phosphate was used as the target absorbate to evaluate possible incorporation of both sulphate and phosphate coexisting in the ettringite structure. This confirmed that the novel idea of incorporating pollution components in a reaction may allow for removing efficiencies that are much higher than obtainable from traditional sorption operation.

Separation of Cu(II) from Cd(II) in sulfate solution using CaCO3 and FeSO4 based on mechanochemical activation

Cadmium and its compounds are important resources in different industries; on the other hand, cadmium is one of the most toxic heavy metals which can cause various health problems. Therefore it is important to develop effective methods for the separation of cadmium from other commonly associated metals from the stance of both resource recycling and environmental purification. Lime neutralization (Ca(OH)2) and ferrite are widely used to precipitate heavy metals. Limestone (calcium carbonate: CaCO3) is too stable to be used directly for this purpose. Mechanochemical activation was introduced to increase the activity of CaCO3. Fe(II)sulfate heptahydrate (FeSO4·7H2O) was used as a selective precipitation agent. As a result, Cu(II) was preferentially precipitated as (Fex,Cuy)O while the Cd(II) remained in the solution. The residual of Cu(II) ions in solution could be controlled at less than 0.1%, meanwhile more than 90% of Cd(II) ions remained in aqueous solution. Then, Cu(II)–Cd(II) separation was achieved by a simple solid–liquid separation.

Transforming Hematite into Magnetite Using Mechanochemical Approach as a Pretreatment of Oolitic Hematite

ABSTRACT Potential transformation of oolitic hematite into magnetite by mixing iron powder using the mechanochemical method has been achieved and discussed in this paper. The phase transition of pure hematite in the preliminary test was identified by X-ray diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The experimental results have shown that the crystallographic planes of magnetite, (220), (311), (400), and (511) were observed clearly in the Fe/α-Fe2O3 mixture after milling for 15 h, indicating that α-Fe2O3 had been effectively transformed into Fe3O4. The diffraction peaks of magnetite were also observed at d = 0.29605 nm (2θ = 30.163°), 0.25226 nm (2θ = 35.559°), 0.24156 nm (2θ = 37.190°), and 0.20898 nm (2θ = 43.458°) after 13 h milling-time. It suggests that the oolitic hematite is transformed into magnetite successfully by mechanochemical processing. The processing might be applied potentially for the magnetic separation of oolitic hematite.

Separation of copper from cobalt in sulphate solutions by using CaCO3

ABSTRACT Lime neutralization is widely used to precipitate heavy metals including copper and cobalt from wastewater. Limestone (calcium carbonate: CaCO3) is too stable to be used directly for this purpose. Grinding of CaCO3 in the solutions of copper and cobalt sulphate was conducted to raise its reactivity. During the mechanochemical activation, CaCO3 reacted with copper sulphate but not significantly with cobalt sulphate and this phenomenon allowed an easy separation of copper from cobalt. The residual of Cu(II) ions in solution could be controlled at less than 0.1%, meanwhile more than 90% of the Co(II) ions remained in aqueous solution.

Potassium fixation and the separation from sodium through the formation of K-alunite using activated aluminum hydroxide

ABSTRACT This report introduces a novel method of separating potassium from sodium by synthesizing K-alunite using activated aluminum hydroxide (Al(OH)3). A two-step operation, consisting of the mechanochemical activation of Al(OH)3 and subsequent hydrothermal processing at a low temperature of 80°C with Al2(SO4)3 · 18H2O and K2SO4 or Na2SO4, was conducted. K-alunite but not Na-alunite at this low temperature was successfully formed, leading to the possible separation of potassium sulfate from sodium sulfate more easily. The process may serve the purpose of recovering potassium from some aqueous alkali sources for providing potash fertilizer in agricultural application.

Aluminous Minerals for Caustic Processing of Scheelite Concentrate

Dry milling of the mixture of scheelite concentrate and solid NaOH is conducted to develop a caustic process for tungsten (W) extraction. Aluminum hydroxide (Al(OH)3) is further added to the milling to control the calcium dissolution of one reaction product, calcium hydroxide, in the next aqueous extraction of soluble tungstate to form an insoluble substance. For practical application, several aluminous minerals of kaolin, gibbsite, and diaspore with different alumina concentrations and water percentages are used to replace the pure chemical Al(OH)3, and the feasibility of using these minerals as calcium immobilization additives is confirmed to give rise to the formation of Na2WO4 and water-insoluble katoite (Ca3Al2(SiO4)3−x(OH)4x) in the form of powders. Tungsten recovery is found to depend on the compositions of the used mineral, and the conditions for improving W recovery are studied with respect to the compositions of aluminum hydroxide and water inside the minerals. The developed process allows the caustic extraction of W by applying the nearby available aluminous minerals.