Making Industrial Processes More Cost Efficient

Mineral Processing

How nonlinear modeling improved hydrometallurgical leaching process

Development of quality mathematical models fit for industrial production processes, particularly leaching, has been considered to be very difficult. However, the results of a recent project illustrate that newer nonlinear modelling techniques have clearly improved the situation.

Mineral leaching processes are often quite complicated even if only one or two chemical reactions cause the leaching. The reactions are usually heterogeneous and can be mass-transfer limited or reaction-rate limited. At a ore processing plant, the main reaction in the leaching process is a three-phase chemical reaction, and there are a few other reactions occurring in parallel leaching metals other than base material. These processes cannot be modelled practically by phenomenological modelling. A large number of variables affect the leaching rate, and therefore impacting yield of the process. Empirical and semi-empirical modeling approaches do not need deep knowledge of the phenomena occurring in the process; it is sufficient to measure the variables of interest. Conventional empirical modeling employs linear statistical techniques, primarily linear regression and its variants. However, most industrial processes do not tend to be very linear. Therefore, nonlinear empirical or semi-empirical modeling is almost always a better alternative to linear techniques.

This article describes the experience of developing nonlinear models of a leaching process used by Norilsk Nickel Harjavalta Oy in Harjavalta, Finland. Theoretical issues are also discussed, followed by a brief explanation of how the nonlinear models were implemented in software suitable for use by plant operators. Norilsk Nickel Harjavalta Oy has years of experience in producing high quality nickel products, including both metals and chemicals, and several of its products are produced by innovative and efficient production processes developed in-house. The company’s product portfolio is diverse, its products have applications in several industrial sectors and are exported to practically all parts of the world from the Harjavalta plant. Even so, its production processes are in continuous development.