Alumina and Silica Produced by Chlorination of Power Plant Fly Ash Treatment
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https://doi.org/10.1007/s11837-020-04267-5 Ó 2020 The Minerals, Metals & Materials Society
ALUMINUM: RECYCLING AND CARBON / ENVIRONMENTAL FOOTPRINT
Alumina and Silica Produced by Chlorination of Power Plant Fly Ash Treatment VALERY KAPLAN ,1,3 NURLAN DOSMUKHAMEDOV,2 ERZHAN ZHOLDASBAY,2 GALAMAT DARUESH,2 and AIDAR ARGYN2 1.—Weizmann Institute of Science, 234 Herzl St., PO Box 26, 7610001 Rehovot, Israel. 2.—Satbayev University, Satbayev St. 22, 050013 Almaty, Kazakhstan. 3.—e-mail: [email protected]
We describe a process of chlorination of fly ash with either chlorine gas or calcium chloride, which successfully decomposes mullite and permits the extraction of a number of industrially useful, acid-soluble compounds. As a guide for determining optimal input molar ratios and temperatures, the Gibbs energies for three groups of reactions of major fly ash components between 973 K and 1473 K were calculated: (1) chlorination with chlorine gas; (2) chlorination with chlorine gas in the presence of coal; (3) chlorination with calcium chloride. Laboratory-scale measurements with fly ash from six coal combustion power plants in Kazakhstan show that chlorination with either calcium chloride or chlorine gas allows efficient extraction of alumina (aAl2O3) and silica with both high yield and purity.
INTRODUCTION Coal-fired power plants in developed countries produce large volumes of fly ash annually, of which more than half is disposed of in dry landfills: India, 112 million tons; China, 100 million tons; USA, 75 million tons; Germany, 40 million tons; Great Britain, 15 million tons.1 In the Russian Federation, there are more than 170 coal-fired power plants, in which 300 million tons of fly ash and slag are produced each year. Over 20,000 km2 of land is currently used for storage of 1.3–1.5 billion tons of fly ash and slag waste from Russian power plants.2 Such storage of fly ash and slag waste presents serious environmental, health and economic problems: fly ash contains hazardous trace elements, including As, B, Cr, Mo, Ni, Se, Sr and V, which can contaminate the environment because of leaching by rain and groundwater.3 The problem of fly ash accumulation and storage is of particular relevance for Kazakhstan, where the development of electricity production in coal-fired power plants is an urgent governmental priority. To date, the total fly ash output from coal burning in this Republic
(Received March 8, 2020; accepted June 30, 2020)
is 19 million tons per year and the amount of fly ash accumulated in landfills exceeds 300 million tons.4 Fly ash from coal-fired power plants is potentially a valuable material for the manufacture of construction materials such as blended cement, fly ash bricks, mosaic tiles and hollow blocks. It also has other high-volume applications and can be used for paving roads, building embankments and mine fills.5 Fly ash particles are fine, amorphous and spherically shaped as a result of the high-temperature pulverizing combustion of solid organic fuels.6 They have an average size of
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