Model of Phosphorus Precipitation and Crystal Formation in Electric Arc Furnace Steel Slag Filters

Abstract

The objective of this study was to develop a phosphorus retention mechanisms model based on precipitation and crystallization in electric arc furnace slag filters. Three slag columns were fed during 30 to 630 days with a reconstituted mining effluent at different void hydraulic retention times. Precipitates formed in columns were characterized by X-ray diffraction and transmission electronic microscopy. The proposed model is expressed in the following steps: (1) the rate limiting dissolution of slag is represented by the dissolution of CaO, (2) a high pH in the slag filter results in phosphorus precipitation and crystal growth, (3) crystal retention takes place by filtration, settling and growth densification, (4) the decrease in available reaction volume is caused by crystal and other particulate matter accumulation (and decrease in available reaction time), and (5) the pH decreases in the filter over time if the reaction time is too low (which results in a reduced removal efficiency). Crystal organization in a slag filter determines its phosphorus retention capacity. Supersaturation and water velocity affect crystal organization. A compact crystal organization enhances the phosphorus retention capacity of the filter. A new approach to define filter performance is proposed: saturation retention capacity is expressed in units of mg P/mL voids.

Removal of phosphate from greenhouse wastewater using hydrated lime

“…It has been reported that Ca-P crystal growth occurred on a steel slag material when settling was allowed, despite highly supersaturated conditions. [37] Overall, further research concerning precipitate physical characteristics (size, settling rate), composition, and use as a fertilizer, is needed. This will help with designing systems that maximize precipitate usefulness as a fertilizer source and minimize loss, without incurring prohibitive costs from increasing system complexity or sacrificing PRE.…”

Modelling constructed wetlands: Scopes and aims – a comparative review

“…Besides displaying process interactions, mechanistic models can also be used to gain in-depth understanding of a particular phenomenon. Some researchers carried out specific simulations for this purpose: Petitjean et al (2011Petitjean et al ( , 2012 and Forquet et al (2009a,b) investigated the influence of the air phase on hydrodynamics (Diph_M), Morvannou et al (2013) focused on non-equilibrium flow in French-type VFCW with the dual-porosity model (DPM), Claveau-Mallet et al (2012, 2014 studied the phosphorus removal by precipitation in steel slag filters (Phydroslag) and Sani et al (2013) investigated particulate transport (Wang-Scholz-Model).…”

“…It is based on slag dissolution and hydroxyapatite (Ca 5 (PO 4 ) 3 OH) crystallization rates. It included three steps: (i) dissolution of slag as Calcium oxide (CaO), (ii) phosphorus precipitation and crystal growth in alkaline conditions, (iii) evolution of slag filter properties (slag dissolution rate, porosity and hydraulic conductivity) related to slag exhaustion and to the presence of crystals (Claveau-Mallet et al, 2012). The conceptual model was mathematically expressed in a 1D geochemical model including equilibrium and rates (Claveau-Mallet et al, 2014).…”

“…The P-hydroslag model can be easily upgraded with additional equations when needed, by example calcite precipitation if the wastewater contains a high concentration of inorganic carbon. The main complexity challenge can be found in the description of crystal structures within the filter affecting the dissolution rate of slag (Claveau-Mallet et al, 2012). As hydroxyapatite crystal structures are diversified (hydroxyapatite is also a biological product!…”

Phosphorus removal structures: A management option for legacy phosphorus

“…Researchers throughout the world have examined various materials that may serve as a PSM in this fashion (Claveau-Mallet et al 2011;Klimeski et al 2012;Vohla et al 2011;Lyngsie et al 2013). While the operational theory of P removal structures is simple, proper design of a structure for specific site conditions and a given lifetime is more involved.…”