Environmental and economic implications of slag disposal practices by the ferrochromium industry: A case study

A large volume of slag is annually produced by the ferrochromium industry and the slag has historically been dumped without any pollution prevention, control or remediation measures. The slag at the ASSMANG Chrome Machadodorp (ACM) plant in Mpumalanga (where this case study was conducted) contains elements that may pose a significant threat to human life and the environment. The objectives of this study were to assess the composition of the slag produced at the ACM plant and classify the slag in terms of the minimum requirements, as prescribed by the Department of Water Affairs and Forestry (DWAF), and to determine the economic implications of compliance with existing statutory requirements, and critically assess the implementation of the minimum requirements in practice. According to leachability results for the ACM slag, aluminium (Al), iron (Fe) and manganese (Mn) have the potential to leach from the slag in excess of the acceptable risk levels. Using the minimum requirements’ prescribed methods, the ACM slag was classified based on these three substances as Hazard Rating II. Total elimination of the production of slag is impossible at this stage and disposal on a permitted H:H landfill site is currently the final waste management option. Permitting and construction of an H:H landfill site to accommodate all the ACM slag produced over a period of 55 years are conservatively estimated at between R 6.2 m. and R12 m. The cost to remove and dispose of 13 × 106 t ACM slag at the Holfontein landfill site is an estimated R5 900 m. If another permitted H:H landfill site becomes available at Nelspruit, the cost will be reduced to an estimated R4 600 m. The DWAF minimum requirements document used for this case study is a useful guideline. However, the document was not compiled for use by a layman and the subsequent application requires careful studying and practice. Furthermore, a number of issues, for example, relevant usage of the two different methods for classification and ascribing a higher hazard rating to substances with high Koc values, require clarification.