『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