Numerical simulations with the P-Hydroslag model to predict phosphorus removal by steel slag filters. (1st December 2017)

• Record Type: Journal Article
• Authors: Claveau-Mallet, Dominique; Courcelles, Benoît; Pasquier, Philippe; Comeau, Yves
• Is Part Of: Water research. Volume 126(2017)
• Page Start: 421
• Page End: 432
• Publication Date: 2017-12-01
• Subjects: Slag -- Phosphorus -- Wastewater treatment modelling -- PHREEQC -- Hydroxyapatite -- Calcite -- Precipitation; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2017.09.032
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: The first version of the P-Hydroslag model for numerical simulations of steel slag filters is presented. This model main original feature is the implementation of slag exhaustion behavior, crystal growth and crystal size effect on crystal solubility, and crystal accumulation effect on slag dissolution. The model includes four mineral phases: calcite, monetite, homogeneous hydroxyapatite (constant size and solubility) and heterogeneous hydroxyapatite (increasing size and decreasing solubility). In the proposed model, slag behavior is represented by CaO dissolution kinetic rate and exhaustion equations; while slag dissolution is limited by a diffusion rate through a crystal layer. An experimental test for measurement of exhaustion equations is provided. The model was calibrated with an experimental program made of three phases. Firstly, batch tests with 300 g slag sample in synthetic solutions were conducted for the determination of exhaustion equation. Secondly, a slag filter column test fed with synthetic solution was run for 623 days, divided into 9 cells and sampled at the end of the experiment. Finally, the column was dismantled, sampled and analyzed with XRD, TEM and SEM. Experimental column curves for pH, oPO4, Ca and inorganic carbon were well predicted by the model. Crystal sizes measured by XRD and TEM validated the hypothesis for homogeneous precipitation while SEM observations validated the thin crystal layer hypothesis. A preliminary validation of the model resulted in successful predictions of a steel slag filter longevity fed with real wastewater. Graphical abstract: Image 1 Highlights: Presentation of a new model for prediction of phosphorus removal by steel slag filter. Presentation of an experimental procedure for measurement of slag exhaustion behavior. Model including equations for slag exhaustion, diffusion into crystal barrier, nucleation and crystal growth. Validation of model equations with microscopic observations (SEM and TEM) and XRD. Numerical simulations reproduces slag filter experimental data.