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.

Graphical Abstract

中文翻译：

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从废铸造砂中回收二氧化硅和脱硅铸造砂的碱活化

摘要

进行这项研究的目的是通过浸出工艺从废铸造砂（WFS）中回收作为有价值的准金属的二氧化硅（硅化作用），并找到脱硅铸造砂（DFS）的应用。浸出时间为5小时；使用3 M的氢氧化钾（KOH）作为浸出试剂。发现200 rpm的搅拌速度和25的液/固比是获得最佳浸出结果的最佳条件。通过使用NaOH作为碱性活化剂开发了DFS的地聚合物。所得结果表明，合成地质聚合物的最佳条件是15 M NaOH，150 µm DFS粒径和80℃的固化温度72 h。地质聚合物强度的提高归因于作为新型水合产物的辉石和钾硅石的形成。在最佳碱性溶液浓度下，最高的无侧限抗压强度（UCS）为4.8 MPa。开发的地质聚合物满足了承重材料的最低强度要求。这项研究为废铸砂的选矿和有价值的准金属的回收提供了一种新颖新颖的解决方案，从而实现了零废物的产生。

图形概要