Abstract
White mud is residue discharged during the acid method in the aluminum extraction process from coal fly ash, and this material is harmful to the environment. The implementation of an environmentally friendly and valuable way to use white mud is a key factor restricting the commercial application of the acid method in the fly ash alumina extraction technology. An analysis of white mud revealed the following: (1) it was highly enriched in SiO2 (70–80%) while concentrations of acid-soluble elements, such as Na, Al, and Fe, and some hazardous heavy metals, including Pb and Cr, were significantly lower than raw fly ash; (2) approximately 80% of SiO2 had relatively high reaction activity because of the foregoing Al-extraction treatment. Through an ingenious green chemical process, the complete conversion of white mud into silicon–calcium fertilizer (SCF) was achieved under very mild reaction conditions (approximately 100 °C and atmospheric pressure). Waste liquor was totally recycled, and no secondary solid waste was generated. The SCF had an available silicon content (ASC) of 35%, significantly higher than the commercial standard (20%). Converting them into soil conditioners or ecological remediation materials with the lowest possible energy consumption and secondary pollution may be the most promising approach for the future disposal of aluminosilicate industrial solid wastes.
Highlights
High alumina coal and coal combustion fly ash in the Zhungeer coal basin in China, a “unique polymetallic artificial deposit,” has attracted increasing attention [1,2,3,4,5]
The ash yield elements and mineral composition of the white mud samples were determined by X-ray fluorescence spectrometry (XRF, ZSX Primus, Rigaku, Japan) and X-ray diffraction (XRD, D8 ADVANCE, Bruker, Germany)
Enrichment of the SiO2 and dilution of the Al2 O3 facilitates the production of high-quality silicon–calcium fertilizer (SCF)
Summary
High alumina coal and coal combustion fly ash in the Zhungeer coal basin in China, a “unique polymetallic artificial deposit,” has attracted increasing attention [1,2,3,4,5]. The amount of aluminum in this high-Al coal and fly ash is estimated to be as high as 10 billion tons of Al2 O3. Attempts to recover aluminum from fly ash can be traced back to the 1950s [6]. Recovery technologies for aluminum from fly ash include the Bayer method (1) [7], a hightemperature chlorination process (2) [8], and the acid-leaching method (3) [9]. Using the Zhungeer high-Al circulating fluidized bed fly ash as a raw material, the China National
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