Simultaneous Determination of Various Phosphates in Water-Soluble Ammonium Polyphosphate

Simple, fast, and simultaneous determination of orthophosphate, pyrophosphate, and tripolyphosphate by capillary electrophoresis with capacitively coupled contactless conductivity detection

This work describes a novel analytical method using capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4D) for simultaneous, simple, and rapid determination of three inorganic phosphates (orthophosphate, pyrophosphate, and tripolyphosphate) widely used as food additives and in pharmaceutical formulations. A background electrolyte composed of 0.5 mol L-1 acetic acid provided fast separation (around 3.0 min) and good separation efficiency and peak resolution. Linearity in the concentration range of 10-500 mg L-1 was confirmed by the coefficients of determination (R2) higher than 0.99. The limits of detection varied from 0.41 to 0.58 mg L-1. The accuracy of the proposed method was assessed by recovery tests conducted at three concentration levels in tap water samples, food, and personal hygiene products. Recovery values varying from 81% to 118% were achieved, indicating an acceptable accuracy. The proposed CE-C4D successfully determined the three inorganic phosphates in the analyzed samples.

Hydrolysis Mechanism of Water-Soluble Ammonium Polyphosphate Affected by Zinc Ions

Ammonium polyphosphate (APP) as a chelated and controlled-release fertilizer has been widely used in agriculture, and its hydrolysis process is of significance for its storage and application. In this study, the hydrolysis regularity of APP affected by Zn²⁺ was explored systematically. The hydrolysis rate of APP with different polymerization degrees was calculated in detail, and the hydrolysis route of APP deduced from the proposed hydrolysis model was combined with the conformation analysis of APP to reveal the mechanism of APP hydrolysis. The results show that Zn²⁺ decreased the stability of the P-O-P bond by causing a conformational change in the polyphosphate due to chelation, which in turn promoted APP hydrolysis. Meanwhile, Zn²⁺ caused the hydrolysis of polyphosphates with a high polymerization degree in APP to be switched from a terminal chain scission to an intermediate chain scission or various coexisting routes, affecting orthophosphate release. This work provides a theoretical basis and guiding significance for the production, storage, and application of APP.

Treatment of distiller grain with wet-process phosphoric acid leads to biochar for the sustained release of nutrients and adsorption of Cr(VI)

Soil amendment products, such as biochar, with both sustained nutrient release and heavy metal retention properties are of great need in agricultural and environmental industries. Herein, we successfully prepared a new biochar material with multinutrient sustained-release characteristics and chromium removal potential derived from distiller grain by wet-process phosphoric acid (WPPA) modification without washing. SEM, TEM TG-IR, in situ DRIFTS and XRD characterization indicated that biochar and polyphosphate formed simultaneously and were tightly intertwined by one-step pyrolysis. The optimal product (PKBC-400) had the most stable carbon structure and an adequate P-O-P structure with less P loss. Batch experiments illustrated that 92.83% P (ortho-P), 85.94% K, 41.49% Fe, 78.42% Al and 65.60% Mg were continuously released in water from PKBC-400 within 63 days, and the maximum Cr removal rate reached 83.57% (50 mg/L K₂Cr₂O₇, pH=3.0) with an increased BET surface area (304.0557 m²/g) after nutrient release. SEM, IC and ³¹P NMR analyses revealed that the dissolution and hydrolysis of polyphosphates not only realized the sustained release of multiple nutrients but also significantly improved the sustained release performance. The proposed resource utilization strategy provided new ideas for Cr hazard control, biomass waste utilization and fertilizer development.

Selective adsorption of various phosphorus species coexistence in water-soluble ammonium polyphosphate on goethite: Experimental investigation and molecular dynamics simulation

The geochemical processes of polyphosphates (poly-Ps) are important for phosphorus (P) management and environmental protection. Water-soluble ammonium polyphosphate (APP) containing various P species has been increasingly used as an alternative P-fertilizer. The various P species coexistence and the chelation of poly-Ps with mental would trigger the P's competitive adsorption and affect the APP's adsorption intensity on goethite, compared to single orthophosphate (P₁). P adsorption behaviors of APP1 with two P species and APP2 with seven P species on goethite were investigated via batch experiments in comparison to the traditional P-fertilizer of mono-ammonium phosphate (MAP). Coadsorption of P₁ and pyrophosphate (P₂) on goethite was investigated by molecular dynamics (MD) simulation. The more Fe³⁺ dissolved from goethite as a bridge due to the chelation of poly-Ps in APP and contributed to the stronger APP adsorption on goethite compared with MAP. Ion chromatography and spectral analysis showed P₁ and P₂ in APP were mainly adsorbed by goethite via mainly forming bidentate complexes. The goethite preferentially adsorbed P₁ at lower APP concentration but increased the poly-Ps' adsorption at higher APP concentration. MD simulation showed that electrostatic interaction and hydrogen bonds played a key role in water-phosphates-goethite systems. The P₁ pre-adsorbed on goethite could be replaced by P₂ at high P₂ concentration. The results develop new insights regarding the selective adsorption of various P species coexistence in goethite-rich environments.

Solid-Liquid Phase Equilibrium of Ammonium Dihydrogen Phosphate and Agricultural Grade Ammonium Polyphosphate (Degree of Polymerization Ranging from 1 to 8) for Mixed Irrigation Strategy

Water-soluble ammonium polyphosphate (APP) has the advantages of good solubility and slow-release characteristics and has the potential to be used in combination with monoammonium phosphate (MAP) as a high phosphorus content slow-release fertilizer to improve the utilization rate of phosphorus during irrigation. Herein, the effects of the APP1 concentration and temperature (278.2-313.2 K) on the solubility of MAP, solution density, and pH value in the ternary equilibrium system (APP1-MAP-water) were measured. The simplified Apelblat model, two empirical polynomials, and rational two-dimensional functions can describe the experimental solubility data, solution density, and pH value well, respectively, with reliable modeling parameters (R ² > 0.99). In the OptiMax1001 reactor, the focused beam reflectance measurement (FBRM), the particle-view measurement (PVM), and the ReactIR 15 probes were used to observe and reverse verify that they can be synergistically codissolved to achieve economic efficiency. Basic thermodynamic data and models can guide their collaborative application in irrigation to improve the phosphorus utilization rate.

Determination of phosphate in water by flow coulometry

In this work, the possibility of flow coulometry application as coulometric titration was studied. The method was used to analyze phosphates in wastewater samples. The principle of the determination consisted in the formation of molybdophosphate and its subsequent one-electron electrolytic reduction. The present method is applicable under optimal conditions in the concentration range of 1.5 × 10−6 to 5.5 × 10−5 mol/dm3. Detection limit of the method is 3.42 × 10−7 mol/dm3. Mineralization step has been proved a problem in total phosphate content determination. If mineralization was not carried out, only inorganic soluble phosphates were determined. It is a new method characterized by its simplicity of instrumentation and handling, which is a prerequisite for its further use in the field of trace analysis.