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.

Fulvic-polyphosphate composite embedded in ZnO nanorods (FA-APP@ZnO) for efficient P/Zn nutrition for peas (Pisum sativum L.).

A nano-fertilizer (FA-APP@ZnO) was designed and prepared based on the copolymer of fulvic acid (FA) and ammonium polyphosphate (APP) with ZnO nanorods embedded, to tackle the antagonism between phosphorus (P) and zinc (Zn) in fertilization. FA-APP@ZnO was confirmed to revert the precipitability of H2PO4 - and Zn2+ into a synergistic performance, where FA and APP can disperse ZnO nanorods, and in return, ZnO catalyzes the hydrolysis of the absorbed APP. The hydrolysis rate constant of pyrophosphates consequently increased 8 times. The dry biomass of pea (Pisum sativum L.) under the FA-APP@ZnO hydroponics for 7 days increased by 119%, as compared with the situation employing the conventional NH4H2PO4 and ZnSO4 compound fertilizer. Moreover, the uptake of seedlings for P and Zn was enhanced by 54% and 400%, respectively. The accelerated orthophosphate release due to ZnO catalysis and the well-dispersed ZnO nanorods enabled by APP met the urgent demand for P and Zn nutrients for peas, especially at their vigorous seedling stage. This work would provide a new idea for constructing nano-platforms to coordinate the incompatible P and Zn nutrients for the improvement of agronomic efficiency.

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.

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.

Purification of Wet-Process Phosphoric Acid via Donnan Dialysis with a Perfluorinated Sulfonic Acid Cation-Exchange Membrane.

This work reports the application of an electromembrane process, Donnan dialysis (DD), for the purification of so-called wet-process phosphoric acid (WPA). Nitric acid is used as the stripping solution to remove metallic cations (mostly Fe3+, Al3+, and Mg2+) that are harmful to the further processing of WPA. The paper first presents a set of experimental data on the measurements of the metallic cation fluxes through a perfluorinated sulfonic acid cation-exchange membrane. Not only WPA, but also synthetic phosphoric acid solutions with mixed metallic cations (MPA) and with a single metallic cation (SPA) were studied. This confrontation confirms (1) that the order of metallic cations fluxes is Mg2+ > Al3+ > Fe3+; (2) that, compared with MPA, the purification effect of WPA causes only negligible change; (3) that, by comparing the DD processes with SPA and MPA solutions, the reason for the low transmembrane fluxes of Fe3+ and Al3+ could be explained by the large ionic charge and large hydrated ion radius. Furthermore, by analyzing the ion composition of membranes equilibrated in SPA solutions, we conclude that the forms of cations in the membrane are most likely Fe3+, Al3+, and Mg2+.

Differences in main processes to transform phosphorus influenced by ammonium nitrogen in flooded intensive agricultural and steppe soils.

Exogenous ammonium nitrogen (AN) fertilization/deposition and the subsequently induced soil acidification, might exacerbate soil phosphorus (P) transformation and mobility, whereas poor understanding in abiotic and biotic processes still existed between intensively cultivated soil with high proportion of legacy inorganic P (Pi) in comparison to natural steppe soil with high proportion of organic P (Po). Column batch flooded experiment using vegetable (VEG) and steppe (STE) soils was conducted to investigate the P transformation and mobility influenced by 60-day intermittent elution with an (1500 mg N kg-1) solution or an acid sulfate (107 mmol H+ kg-1) solution. The results showed that AN elution significantly decreased the contents of all Pi fractions and strengthened Pi leaching, whereas acid elution increased the contents of Al-Pi, Fe-Pi, and reductant-soluble Pi and reduced P leaching in VEG soil. In contrast, AN elution increased the contents of soluble-Po and Al-(Pi + Po) and decreased Ca-P and Fe-Pi, no effects on P leaching, whereas acid elution increased the contents of soluble-(Pi + Po), Al-(Pi + Po), Fe-(Pi + Po) and reduced P leaching in STE soil. Variances analysis showed that pH and microbial biomass carbon were the most important factors to predict the P composition of the VEG and the STE soil, respectively. This indicated that AN elution released the soil mineral-bound phosphate with ammonia oxidation coupled with Fe(III) reduction, besides the same chemical influences on Fe/Al oxides as acid elution in VEG soil; while predominantly affected biochemical/biological processes of soil P by changing microbial biomass and enzyme activities in STE soil.

Manure and nitrogen application enhances soil phosphorus mobility in calcareous soil in greenhouses.

Over many years, high phosphorus (P) loading for intensive vegetable cropping in greenhouses of North China has contributed to excessive P accumulation, resulting in environmental risk. In this study, the influences of manure and nitrogen (N) application on the transformation and transport of soil P were investigated after nine years in a greenhouse tomato double cropping system (winter-spring and autumn-winter seasons). High loading of manure significantly increased the soil inorganic P (Pi), inositol hexakisphosphate (IHP), mobile P and P saturation ratio (PSR, >0.7 in 0-30 cm depth soil; PSR was estimated from P/(Fe + Al) in an oxalate extract of the soil). The high rate of N fertilizer application to the studied calcareous soil with heavy loading of manure increased the following: (i) mobile organic P (Po) and Pi fractions, as evidenced by the decrease in the ratio of monoesters to diesters and the proportion of stable Pi (i.e., HCl-Pi) in total P (Pt) in 0-30 cm depth soil; (ii) relative distribution of Po in the subsoil layer; and (iii) P leaching to soil depths below 90 cm and the proportion of Po in Pt in the leachate. More acidic soil due to excessive N application increased P mobility and leaching. The increase in Ox-Al (oxalate-extractable Al) and the proportion of microbe-associated Po related to N application at soil depths of 0-30 cm suggested decrease in the net Po mineralization, which may contribute to downward transport of Po in the soil profile.

Phosphorus in China's Intensive Vegetable Production Systems: Overfertilization, Soil Enrichment, and Environmental Implications.

China's vegetable production has experienced a rapid growth in recent years. Total production amounted to 522.7 million Mg (1 Mg = 10 g) in 2009, which was more than nine times that in 1980 and represented >50% of the world production. Meanwhile, excessive use of animal manures and chemical fertilizers in vegetable fields has brought various production and environmental challenges, including excessive accumulation of nutrients in soils and accelerated water pollution problems. In this study, we have evaluated the current status of phosphorus (P) in China's intensive vegetable production systems based on data summarized from nearly 100 publications plus results from our recent experiments. Gross overfertilization occurred in greenhouse (571 kg P ha) and open-field (117 kg P ha) vegetable systems compared with P removal in harvested crops (44 and 25 kg P ha) per season. Excess P input led to soil enrichment of labile P, measured as Olsen-P, averaging 179 (greenhouses) and 100 mg P kg (open fields) in the 0- to 20-cm soil depth, and in some cases led to P leaching, as evidenced by increases in Olsen-P and CaCl-P at the 40- to 60-cm soil depth. The vast majority of vegetable soils had Olsen-P exceeding the critical level (46.0-58.0 mg P kg) for optimum vegetable yield. Innovative policies and strategies are urgently needed to implement science-based nutrient management practices to attain sustainable vegetable production while protecting natural and environmental resources.