In the process of copper extraction in cobalt hydrometallurgy, the copper concentration of raffinate solution needs to be monitored and controlled simultaneously. It is difficult to measure such concentration online by existing instruments and sensors. Soft sensor technique has been became an online supplement measurement for process monitoring and control. In this paper, an adaptive hybrid modeling method for copper extraction process is proposed. The proposed model is composed of simplified first principle model and block-wise recursive PLS model. The former based on material balancing calculation with some assumptions is used to describe the extraction process in general; and the latter is constructed to compensate the unmodeled characteristic and deal with the time-variant feature. A model rectification strategy is also employed to correct the final output and increase the prediction accuracy. The proposed model has been used in a cobalt hydrometallurgy pilot plant, and the prediction results indicate that the adaptive hybrid model is more precise and efficient than the other conventional models. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.