Mini-series on material balance – Part 2: Material balancing throughout the process life-cycle

Discover a CASPEO mini-series dedicated to the material balance in mineral processing: the material balance, a key step between measurement and process control. A treatment process of mineral raw material is subject to design, sizing, construction, production, adaptation and finally dismantling. The material balance is the guideline of this process. In this second part, learn how material balancing could be used throughout the process life-cycle.

The predictive material balance

From the very first laboratory tests, the material balance is the basis of all performance calculations, including kinetics, whether for particle size reduction, classification, concentration, solid-liquid separation, or hydrometallurgical and pyrometallurgical tests. Measurement is often limited, , wrongly, to the only quantities that are strictly necessary, the other quantities, unmeasured, being recalculated using the material conservation laws .

The tests make it possible to define other laws on material quantities, in addition to the conservation laws. For example, in a concentration test, a yield is determined that relates the amount of ore in the concentrate to the amount in the feed. Similarly, recovery relates the quantity of a component in the concentrate to its quantity in the feed. Thus, knowing these performance parameters and the quantities of material in the feed of a concentration operation, the quantities of material in the concentrate and tailing streams can be deduced. This is known as the predictive material balance.

The performance laws, derived from various theories, sometimes empirical, are most often parametric and constitute a mathematical model of the operation. The tests then make it possible to check the validity of these laws in the  particular case studied and, if they are verified, to determine the parameters. The objective of the predictive material balance is then to calculate by simulation all the material streams of a process from its feed. Knowing the performance laws of the various transformation operations and those of conservation, and assuming a sequence of these operations, the output streams can be calculated iteratively as a function of the input streams.

Designing and sizing a processing plant

Performance laws are most often linked to the size of the equipment performing the processing operations. Therefore, based on the desired capacities, it is possible to size a plant and estimate the consumption of reagents, utilities, and wear parts. Modelling and simulation tools for mineral processing have been developed over the last 40 years. They offer the possibility to obtain a complete and detailed material balance and to estimate e parameters that laboratory tests do not provide directly. This is the case for circulating loads, which are too often underestimated, leading to design errors such as undersizing.

The same predictive material balance can therefore be used for the design and sizing of a pilot plant on which tests will be carried out providing a material balance and performance estimates. The results reinforce the knowledge and validity of the laws allowing, still with the help of modelling and simulation, the design and sizing of the industrial plant. The complete and detailed material balance is then essential for good and detailed engineering.

Planning and production assessment

In the production phase, the material balance is used for two purposes: planning and production assessment. Planning is based on a forecast balance, the models of which are generally limited to the performances usually observed associated with conservation laws. Here again, it is important to know the quantities and qualities of raw materials to be processed, finished products, materials in movement or in stock, throughout the planned period. The objective is to meet demand, estimate costs and revenues, and thus seek to maximise profit. Several scenarios can be considered based on metal and consumable price forecasts in order to react more quickly to market changes.

Throughout the operation of the plant, it is necessary to carry out production assessments. These are carried out on different time scales: in near-real time for advanced control systems, by shift or by day to anticipate deviations, by week or by 10-days for the evaluation of production teams, and by month for financial reports. For all these cases, it consists of an observation, based on the measurements performed at the various control points, combined with a reconciliation of data by material balance, leading to a precise, complete, and coherent quantification of all the material movements and stocks, whether in terms of quantity (mass) or quality (content, proportions). It is on these production balances that we will focus our attention in the next article. Stay connected!

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