(41e) Chemsheet As a Simulation Platform for Modelling Industrial Concentrates and Brines

Industrial concentrates and brines are usually a complex mixture of metal ions, anions, gases and precipitates within aqueous media. Typical metals found in these waters are sodium, potassium, iron, calcium, magnesium, manganese, zinc, copper and nickel. Corresponding anions are those associated with e.g. carbon, sulfur and chlorine. In a practical (multiphase) system, the respective gaseous components will also affect the solvent-solute interactions. In industrial applications, temperatures will vary, most typically from ambient 20 °C up to 95 °C in atmospheric systems. Within the concentrated solutions, wanted or unwanted precipitates may occur. Therefore, these mixtures can be considered as true multi-phase chemical systems, which need to be properly understood in order to design, engineer and operate these processes successfully.

Concentrates and solutions descending from industrial side streams still form a challenge for designing environmentally sustainable processes. The problem is common for many industries ranging from mining and minerals processing to chemical and forest industries. The changes in environmental regulations as well as the opportunities to develop new businesses increase the need to develop proactive methods for recycling chemicals and for elimination of environmental hazards. The necessary techniques frequently contain technological solutions and conditions that are very different from those in the main product line. Examples of practical industrial processes include i) handling of mine waters and neutralisation sediments, ii) recovery and recycling of chemicals within metal, chemical and forest industries, iii) scrubbing techniques of flue gasses, iv) in-line precipitation and crystallisation technologies, and v) new energy technologies exploiting concentrates. In order to overcome these challenges, ChemSheet as an agile tool for process modelling was developed.

Methodology

ChemSheet [1] is a process simulation software used for modelling a thermodynamic multi-phase multi-component systems such as industrial concentrates and brines. ChemSheet is used as an Add-in within Microsoft Excel allowing rapid development of models for various phenomena, reactors and reactor networks. The back-end of ChemSheet is state-of-art thermodynamic equilibrium solver ChemApp [2]. The capabilities of this solver are extended within ChemSheet by introducing immaterial constraints [3,4] to the calculation of thermodynamic equilibrium. This unique feature of ChemSheet allows calculating local partial thermodynamic equilibria constrained by extent of reactions or affinities, surface area or volume and electrochemical potential. Concentrate and brines in industrial processes reach seldom thermodynamic equilibrium, and thus such constraints are common when observing industrial processes. Dissolution and precipitation kinetics, membrane processes, and fibrous suspensions are typical examples where constrained thermodynamic models within ChemSheet are utilised.

Suitable thermodynamic data of concentrates and brines is also needed. An aqueous database was developed [5] concurrently with ChemSheet. This database describes common cations (Na⁺ , K⁺ , Ca²⁺ , Mg²⁺, Al³⁺, Fe³⁺ , Cu²⁺ , Mn²⁺) and anions (sulfates, carbonates and chlorides) observed in concentrates and brines. Database utilises Pitzer activity formalism [6] and is applicable solutions up to 6 M. Salient feature of this database is the temperature dependence of parameters. Therefore, database allows modelling many ions within the temperature range 25-95°C. This database is applicable in many industrial cases as common ions in aqueous solutions are often same independent to the field of industry.

Results

Several successful industrial applications are reviewed: i) Lime, limestone and ettringite based neutralisation of acidic mine water (AMD) for controlling the sulfate content of effluent [5] was assessed. Models allowed predicting chemical consumption, required pH levels, sulfate concentrations and the amount and compositions of precipitates and effluents. ii) Optimisation of hydrometallurgical processes and chemical usage [5] was conducted using ChemSheet. Here various alkalis were evaluated and the effect to process conditions was observed during simulation. Tools allowed rapid screening of various process concepts. iii) Calcium carbonate chemistry within paper machine was controlled using ChemSheet based approach [7,8]. Here thermodynamic database was extended with second aqueous phase describing the solution inside the fibres. Constraint based on osmotic coefficients and fixed acidic groups inside fibres were set to model. In addition, the kinetics of CaCO₃ precipitation and dissolving as well as CO₂ release and dissolving were implemented as part of the thermodynamic model. iv) Controlling PCC precipitation by observing the reaction affinities of constrained thermodynamic equilibrium [9]. ChemSheet models allowed controlled in-situ precipation of PCC within fibrous suspension and reduced scaling on the surfaces of pipes.

Summary

ChemSheet was used for defining alternative chemical dosage strategies, for pH and solubility control, and for evaluating optional process concepts in several industrial cases, which are various aqueous solutions, concentrates and brines were processed. The models provide a fast and inexpensive tool for both troubleshooting and problem solving as well as for developing new economical and environmentally benign approaches for industrial concentrates and brine management.

The rapid development of process models through familiar user interface, extending thermodynamic equilibrium calculations with constraints, and a special database for modelling industrial concentrates and brines in elevated temperatures make ChemSheet a unique tool. Several successful Cleantech applications reported so far encourage usage of ChemSheet for solving practical problems related aqueous solutions but also beyond [10].

References

[1] Koukkari, P., Penttilä, K., Hack, K. and Petersen, S., "CHEMSHEET – An Efficient Worksheet Tool for Thermodynamic Process Simulation", In: Microstructures, Mechanical Properties and Processes, Y. Bréchet (Ed.), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim (2005).

[2] Eriksson, G. and Königsberger, E., "FactSage and ChemApp: Two tools for the prediction of multiphase chemical equilibria in solutions", Pure Appl. Chem., 80(6):1293–1302 (2008).

[3] Pajarre, R., Koukkari, P. and Kangas, P., "Constrained and extended free energy minimisation for modelling of processes and materials", Chem. Eng. Sci., 146:244–258 (2016).

[4] Keck, J.C., "Rate-controlled constrained-equilibrium theory of chemical reactions in complex systems", Prog. Energy Combust. Sci., 16(2):125–154 (1990).

[5] Pajarre, R., Koukkari, P. and Kangas, P., Industrial and mine water chemistry - Advanced aqueous database for modelling industrial processes, VTT Technol. 321 (2018).

[6] Pitzer, K.S. and Mayorga, G., "Thermodynamics of electrolytes. II. Activity and osmotic coefficients for strong electrolytes with one or both ions univalent", J. Phys. Chem., 77(19):2300–2308 (1973).

[7] Koukkari, P., Pajarre, R. and Pakarinen, H., "Modeling of the Ion Exchange in Pulp Suspensions by Gibbs Energy Minimization", J. Solution Chem., 31(8):627–638 (2002).

[8] Kalliola, A., Pajarre, R., Koukkari, P., Hakala, J. and Kukkamäki, E., "Multi-phase thermodynamic modelling of pulp suspensions: Application to a papermaking process", Nord. Pulp Pap. Res. J., 27(03):613–620 (2012).

[9] Koukkari, P., Secondary, C.A., Author, C., Koukkari, P., Pajarre, R., Kangas, P., et al., "Monatshefte für Chemie - Chemical Monthly Thermodynamic Affinity in Constrained Free Energy Systems Thermodynamic Affinity in Constrained Free Energy Systems", (n.d.).

[10] Penttilä, K., Salminen, J., Tripathi, N. and Koukkari, P., "Chemsheet as a Simulation Platform for Pyrometallurgical Processes", In: Celebrating the Megascale, John Wiley & Sons, Inc., Hoboken, NJ, USA (2014).