Characterization of Foundry Waste Sand Streams for Recycling Applications in Construction Industry

The local South African foundry industry discharges large volumes of waste sand each year, with estimates for silica and chromite sands of 250,000 and 25,000 tons, respectively. As a developing country, South Africa is moving toward a greener environment, so the management of industrial waste is an imperative area of study. In this work, we present the laboratory analysis results of the characteristics of three waste sand streams (molding, shot blast, and dust) and discuss the feasibility of reuse options in the construction industry (including concrete mix and cement manufacturing). The results reveal that each stream has its own characteristic properties. In addition, we determined the effect of the molding binder on waste sand, especially on the shakeout sand stream. The results also demonstrate that resin knock sand features much coarser grains and less clay, sulfate, and organic content than greensand. We found the chemistry of sand stream to have the same main constituents as cement kiln feed. With respect to recycling options, we determined that the shakeout stream can be reused in both concrete mix and cement manufacturing. However, special precautions should be taken regarding the clay content of sands originating from greensand foundries. Due to its finer grain size, dust streams can only be recycled in cement manufacturing. Lastly, we found that shot blast sand failed to comply with the requirements of any of the explored recycling options due to it high density, low silica content, and high metallic debris content. The effective beneficiation of sand may involve waste stream segregation and particle size classification since the recycling options we explored (concrete mix) mainly depend upon aggregate size and the impurities present (metallic debris).