The transition towards circular flows within industrial processes often involves assessment of only one type of flow. For example, zero liquid discharge sometimes focuses on water flows, without taking into consideration solid residues. It could however be possible to simultaneously optimize different types of resources, and consequently generate a higher economic yield, a reduced risk, and a reduced environmental impact. The purpose of this study was to find the best use for the solid residues from a zero liquid discharge wastewater treatment at a copper smelting plant. The result was a methodology for resource optimization, based on the principles of reduce, replace, reuse and recycle. The methodology involves relatively simple steps and could be used as a set of instructions for anyone working with resources in almost any industrial process. This methodology is expected to lower one barrier towards a more circular economy - by focusing on preventable losses of valuable resources in all forms (energy, water, and material) and by being simple to use, thereby improving the attitude and knowledge in industrial organizations. With the help of this methodology, it was concluded that the solid waste from the case study could be reduced by 58%–85%. A preliminary economic analysis showed that the operational cost for the optimized waste handling scheme is lower than in the base scenario. If all the proposed changes are fully realizable, the reduced waste will be a result of reduced use of resources in the process, reused resources within the process, and recovered resources which could be recycled and sold as by-products.