Industrial goethite is a by-product occurring during the zinc production process. Although goethite contains a relevant amount of valuable metals, it also creates environmental threats due to the presence of heavy metals and sulphur. While metals recovery from goethite is technically feasible, it is not economically viable with the current technologies.
Hence, today goethite is mostly landfilled in tailing ponds, with considerable economic costs and significant environmental risks. Therefore, academic and industrial research is currently focused on finding technically and economically viable alternatives to goethite landfilling.
In the region of Flanders, north of Belgium, a new zero-waste strategy has been recently proposed, as a result of a collaboration between government, universities and local zinc producers. This new strategy is based on an innovative process, which aims to recover the valuable metals contained in the goethite and to produce new goethite-based construction materials.
However, the environmental burdens connected the proposed recycling process may overtake the environmental or economic benefits. Therefore, the present study analyses the environmental performances of the proposed goethite recycling process, which consists in a sequence of two processes (i) submerged plasma fuming and (ii) inorganic polymerization of the fumed slag.
In the plasma fuming, the goethite is heated up to 1100 °C and valuable metals are recovered through the fumes. The fumed slag undergoes a process of inorganic polymerization, which forms inorganic polymers that can be used as a novel building material, representing an alternative to traditional concrete made with Ordinary Portland Cement (OPC).
Life Cycle Assessment (LCA) is a method for estimating the environmental impacts attributable to the life cycle of a product or a process. In the study, life cycle assessment (LCA) is used to compare the environmental performance of a goethite based inorganic polymer with the environmental performances of an equivalent OPC-concrete. No initial impact coming from the zinc production is allocated to the goethite, as today the goethite is considered as a waste product.
The LCA results show the trade-off between the environmental burdens of the fuming process and inorganic polymerisation versus the environmental benefits of metals recovery, OPC concrete substitution and the avoidance of goethite landfilling. Goethite valorisation showed significantly better environmental performances in terms of several environmental impact categories, thanks to the metals recovery and OPC concrete substitution. The LCA results highlighted also the environmental hotspots to be carefully considered when implementing the goethite recycling. In terms of carbon footprint, the goethite recycling is strongly affected by the high-energy requirements of the fuming process, resulting in high greenhouse gases emissions. The study suggests that a switch towards more efficient and clean energy sources can indeed significantly lower the carbon footprint of recycling. This will make goethite valorisation a sustainable alternative in goethite management, stimulating the implementation of circular economy and zero-waste practices among zinc producers.
Keywords: industrial goethite valorisation, plasma fuming, inorganic polymerisation, LCA
5c. Circular economy, zero waste & innovation
