1. Method for controlling a material separation process, comprising the steps of: measuring at least one process output variable in said material separation process that is indicative of the degree of separation between a desired material and an undesired material, estimating the state of the process at a certain instant in time by applying the measured output variable and external constraints for a prediction time interval on a model of the material separation process, said model being based on at least one input variable that can be manipulated at least two output variables comprising said measured output variable, optimising an objective function that involves at least one predicted controlled process output variable and said external constraints, where said predicted controlled process output variable is defined by said process model based on said state and this optimising takes place under constraints imposed by said process model and/or said external constraints through adapting said input variables, which provides at least one set point value for each input variable for said prediction time interval, characterised in that the method further comprising the step of: regulating said separation process by using said set point value in order to influence the separation process for separating the desired material from bulk material, wherein said step of optimising comprises maximising the recovery of the desired material in the separation process or minimising the amount of additives or the amount of energy used.