Mechanochemical conversion of chrysotile asbestos tailing into struvite for full elements utilization as citric-acid soluble fertilizer

Abstract

Chrysotile asbestos tailing (CAT) are rich in magnesium and silicon which are of great value for crop growth. In this work, CAT was transformed to struvite and silicate salt for the first time by one-step milling with phosphates (NH4H2PO4, (NH4)2HPO4, KH2PO4 and CaHPO4) for full elements utilization as citric acid soluble fertilizer (CASF). The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG) and Scanning electron microscopy (SEM) were used to characterize the obtained samples. The nutrients release data revealed that CAT milling with (NH4)2HPO4 and CaHPO4 was optimal for the production of Mg, N, P, and Si compound CASF which released 0% Mg, 9.37% N, 2.02% P, and 9.86% Si in water and 94.54% Mg, 96.79% N, 96.97% P, and 14.02% Si in 2% citric acid. The prepared product held the nutrients by the mechanism of struvite crystallization in water and released the nutrients by acid-dissolution in citric acid solution. Techno-economic analysis proved the feasibility and economic value of the CASF produced by the proposed mechanochemical approach. This facile and environmentally friendly process would surely contribute to the improvement of resource utilization efficiency and create a sustainable and environmental friendly agricultural production system.