Ore feed to western U.S. phosphate processing plants has variable composition that is reflected in different flocculating behavior. The objective was to model different behaviors so that flocculent consumption could be reduced in a control system. The procedure was first to use molecular dynamics to calculate the influence of ore surface chemistry on flocculent adsorption. These molecular dynamics calculations were then used to modify a baseline transfer function extracted from the thickener of an operating phosphate concentrator. We assumed that calculated adsorption activation energy was related to the experimentally observed thickener transfer function gain. The transfer function was then used to simulate cumulative flocculent use for different flocculent adsorption rates. The results were that with adaptive optimal control approximately half the flocculent could be saved. We concluded that molecular dynamics calculations gave useful insights for adaptive control and thickener efficiency. (C) 2003 Elsevier B.V. All rights reserved.