Recovery of Silicon Dioxide from Waste Foundry Sand and Alkaline Activation of Desilicated Foundry Sand
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RESEARCH ARTICLE
Recovery of Silicon Dioxide from Waste Foundry Sand and Alkaline Activation of Desilicated Foundry Sand Tebogo Mashifana1 · Thandiwe Sithole1 Received: 14 May 2020 / Accepted: 8 October 2020 © The Author(s) 2020
Abstract This study was conducted to recover silica (desilication) as a valuable metalloid from waste foundry sand (WFS) by a leaching process and to find application for desilicated foundry sand (DFS). The leaching time applied was 5 h; 3 M of potassium hydroxide (KOH) was used as a leaching reagent. The agitation speed of 200 rpm and the liquid/solid ratio of 25 were found to be the best conditions for optimum leaching results. A geopolymer from DFS was developed by using NaOH as an alkaline activator. The results obtained showed that the optimum conditions for the synthesis of a geopolymer were 15 M NaOH, 150 µm DFS particle size, and a curing temperature of 80 ℃ for 72 h. The geopolymer strength development was due to the formation of Phillipsite and Kalsilite as new hydration products. At the optimum alkaline solution concentration, the highest unconfined compressive strength (UCS) of 4.8 MPa was achieved. The developed geopolymer met the minimum strength requirements for load bearing material. This study provides an innovative and novel solution for the beneficiation of spent foundry sand and the recovery of a valuable metalloid, resulting to zero waste generation.
The contributing editor for this article was João António Labrincha Batista. * Tebogo Mashifana [email protected] 1
Department of Chemical Engineering, University of Johannesburg, P.O. Box 17011, Doornfontein 2088, South Africa
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Vol.:(0123456789)
Journal of Sustainable Metallurgy
Graphical Abstract
Keywords Desilication · Geopolymer · Resource recovery · Spent foundry sand · Waste beneficiation
Introduction The high amount of waste foundry sand (WFS) produced in South Africa and the high disposal costs have necessitated the development of a solution to deal with the waste generated. WFS has been the focus of extensive research in recent years. South Africa has been reported to have more than 200 casting facilities [1]. The foundry industry generates approximately 350,000 tons of silica sand [2]. Due to the land issue the country is facing, the environmental pollution as a result of the wastes, and the high penalties the foundry industry pay for the disposal of spent foundry sand, the dumping of wastes on the landfill has become a problem for most of these foundry industries. When compared to other countries, the country is facing an over prize for waste disposal, whereby approximately R 63.91 is applicable for disposal in United Kingdom and R505.43 in South Africa [2]. About 3,000 foundries in the United States of America utilize 100 million tons of sand, which result in generating 6–10 million metric tons of foundry waste that is discarded to the landfills annually [3, 4]. Between 2012 and 2013, 9.3 million metric tons of WFS was reported [5]. From a sustainability perspective, the reuse of WFS to b
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