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The component concentrations of sodium aluminate solution are important indices in alumina processing. At present, they are obtained by laboratory titration on samples taken from the production process. Due to the delays in taking and testing samples, they cannot be used for real-time control and optimization. Existing online measurements are not adopted because of the characteristics of the sodium aluminate solution such as high viscosity and the ease of precipitation which leads to pipeline blocking and decreased precision. In this paper, a new modeling method is proposed to measure the component concentrations online using the measurements of conductivity and temperature. The method combines the partial least squares (PLS) technique and the Hammerstein recurrent neural networks (HRNN), where a stable learning algorithm with theoretical analysis is given for the HRNN model. For this PLS-based HRNN, the PLS technique is used to solve the high dimensional and correlated data. Meanwhile, the HRNN technique is used to fit the nonlinear and dynamic characters of the process. An industrial experimental study on a sodium aluminate solution is described. The experiment results show that the proposed method is sufficient to warrant further evaluation in industrial scale experiments.