Miyittah,M.K., Godekar,S., Pullammanappallil,P., Stanley,C.D., Bonzongo,J.-C. and Rechcigl,J.E.(2012): Application of Polymath chemical equilibrium simulation model for struvite precipitation in soils. Water Air Soil Pollut., 223, 1995-2005.

『土壌中のストルーバイト沈殿に対するポリマス化学平衡シミュレーションモデルの適用』


Abstract
 A new speciation model developed and implemented in Polymath was found to be successful in predicting struvite precipitation in soils. Struvite (NH4MgPO4) has been identified as a mineral for the recovery of nitrogen (N) and phosphorus (P). Predicting struvite precipitation potential in soil is important for optimal quantification of nutrient species. Polymath and Visual Minteq models were used for prediction of several solid phases in the soil. One approach to immobilize P for solid-phase formation is by co-blending. Immobilization was achieved through the blending of an Al-based water treatment residual (Al-WTR) and with Ca-Mg-based materials [slag and magnesium oxide (MgO)]. The results suggest that Polymath model revealed solid Phases of dicalcium phosphate pentahydrate (DCPP), magnesium hydroxide (MHO), magnesium orthophosphate (v) docosahydrate (MP22), magnesium orthophosphate (v) octahydrate (MP8), and struvite, which were lacking in the modeling from Visual Minteq. Residual leachate from the co-blended amendments; Soil+WTR+Slag, Soil+WTR+MgO、Soil+MgO, Soil+Slag, Soil+WTR, and the control (without amendment) had struvite of 353, 199, 119, 90, 37, and 12 mg l-1, respectively. This implies that struvite, a phosphate mineral can be precipitated in the soil and could be released as nutrients for plant uptake. Struvite precipitation in soil and for reuse may reduce cost and may be a safe practice for sustainable environmental nutrient management.

Keywords: Struvite; Manure-impacted soil; Phosphorus; Chemical equilibrium modeling』

1. Introduction
2. Materials and methods
 2.1. Soil and amendments characterizations
 2.2. Soil extractions, co-blending, and leaching
 2.3. Chemical equilibrium speciation modeling
 2.4. Chemical equilibrium modeling with polymath
3. Results and discussion
 3.1. Amendments, soil, and leachate composition
 3.2. Simulation vs. experimental data using Polymath model and Visual Minteq
  3.2.1. Solid-phase equilibria from the literature
  3.2.2. Solid-phase equilibria of co-blended soil with Visual Minteq
  3.2.3. Solid-phase equilibria of co-blended soil with Polymath model
4. Conclusions
References


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