Zhiwu Lei

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.

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.

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.