Increase of efficiency in phosphate recovery by understanding the interaction of flow and loading processes with modeling and simulation

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The essential and non-substitutable nutrient, phosphate, is an important fertilizer in agriculture. Industrial recovery processes play an important role in fertilizer production. A phosphate content of the fertilizer of at least ten percent, based on phosphorus pentoxide, has to be ensured in accordance with the requirements of the Fertilizer Ordinance of December 2012. Currently, many processes do not meet these requirements. The P-RoC process (phosphorus recovery from waste water by crystallization) is a promising one, where dissolved phosphate from the aqueous phase binds to particles of porous calcium silicate hydrate (C-S-H). C-S-H particles are easy to dewater and can be used directly as fertilizers when loaded. The uptake process takes place in a stirred reactor, is dynamic and depends on factors such as currents, spatial distribution of particle and phosphate concentrations. The influence of the factors on the efficiency of the process is not fully understood, nor is the kinetics of the reaction. The investigation of the reaction and process kinetics under consideration of the dynamic processes by means of numerical flow simulation poses a challenge not only because of the multi-scale nature, but also has a great potential to improve the process. The aim of the project is to clear up the extent to which the dynamic flow and reaction processes and in particular their interaction influence the phosphate uptake. The aim is also to determine the model equations of the kinetic by means of numerical investigations. This will provide a fundamental and new insight into a calculation of reaction kinetics detached from empirically determined parameters and their direct use in flow simulation to predict the phosphate uptake process of the C-S-H particles.In the planned project, the reaction kinetics of the nanoscale reaction process at the CSH particles is to be captured by means of modelling using a molecular dynamic approach and suitable potential equations at the pore or particle surface. This will be discretized and simulated using a coarse-grained model, based on a discrete element method (DEM), for the substance system phosphate and C-S-H. The reaction kinetics obtained are transferred to the micro- and macro-scale flow simulations and coupled with the lattice Boltzmann methods (LBM). The validation is carried out by literature comparison as well as existing and prepared laboratory experiments. All investigations will be performed by simulations based on the LBM and the DEM with the open source software OpenLB. This enables the implementation of hydrokinetic and coarse-grained modelling within a uniform framework and at the same time ensures a transfer to other questions in connection with reaction kinetics to be determined.