The principal objective of this paper is to introduce simulated annealing to the synthesis of flowsheets in metallurgy and minerals processing. This optimisation methodology will be discussed initially followed by the development of synthesis models for minerals processing and metallurgical flowsheets incorporated in the simulated annealing framework. In a recent paper by the authors a methodology was developed by which complex metallurgical process routes can be synthesised as a function of various ecological, technological and economical aspects. In that paper, however, the process routes were based on the flow of one element only. Therefore, a further objective of this paper is to expand this proposed eco-techno-economic synthesis procedure to incorporate any number of elements by the introduction of simulated annealing as the optimisation procedure.