Decomposition Of Struvite Research Articles

First experimental evidence of the piezoelectric nature of struvite

In this paper, we present the first experimental evidence of the piezoelectric nature of struvite (MgNH4PO4·6H2O). Using a single diffusion gel growth technique, we have grown struvite crystals in the form of plane parallel plates. For struvite crystals of this shape, we measured the piezoelectric coefficients d33 and d32. We have found that at room temperature the value of piezoelectric coefficient d33 is 3.5 pm/V, while that of d32 is 4.7 pm/V. These values are comparable with the values for other minerals. Struvite shows stable piezoelectric properties up to the temperature slightly above 350 K, for the heating rate of 0.4 K/min. For this heating rate, and above this temperature, the thermal decomposition of struvite begins, which, consequently, leads to its transformation into dittmarite with the same non-centrosymmetric symmetry as in case of struvite. The struvite-dittmarite transformation temperature is dependent on the heating rate. The higher the heating rate, the higher the temperature of this transformation. We have also shown that dittmarite, like struvite exhibits piezoelectric properties.

Thermal decomposition of struvite pellet by microwave radiation and recycling of its product to remove ammonium and phosphate from urine

The precipitation of struvite (MgNH4PO4·6H2O) consumes many chemicals to completely remove ammonium and phosphate from urine and has the difficulty in solid separation from solution. This study proposed an alternative approach for the complete nutrient removal through recycling use of microwave-induced decomposition product of struvite pellet with sizes of 2–4 mm. Results showed that microwave radiation effectively decomposed the struvite pellet in an alkaline solution within 8 min. An increase in microwave power and NaOH concentration enhanced the decomposition. The double-layer structure of the pellet led to multiple paths of struvite decomposition. Active components of the decomposition product were newberyite, brucite, and amorphous MgNaPO4 and MgHPO4. The removal efficiencies of ammonium and phosphate from urine both reached 93% using the decomposition product at optimized P/N ratio and pH. Maximum recycles of 4 were recommended because further decomposition of the regenerated struvite pellets induced high losses of magnesium and phosphate. Calculations showed that the total cost of chemical consumption of the proposed approach was reduced by 47% compared with that of a conventional chemical struvite precipitation. Moreover, the volume index of the regenerated struvite pellets was 15 mL/gP which was much lower than that of conventional struvite fines (116 mL/gP), thereby indicating a better solid-liquid separation ability. Therefore, recycling of struvite pellets combining with microwave decomposition was chemical saving and easily separating of solid from liquid for the complete removal of nutrients from urine.

Thermodynamic Analysis of Solid Oxide Fuel Cell Integrated System Fuelled by Ammonia from Struvite Precipitation Process

AbstractEnergy and exergy performance of ammonia fuelled solid oxide fuel cell (SOFC) integrated system in wastewater treatment plants (WWTPs) is evaluated in this study. Ammonia can be recovered through a struvite precipitation process in the form of an ammonia‐water mixture (with 14 mol.% ammonia) and used as a carbon‐free fuel. A series of experiments has been conducted for SOFC single cell to evaluate the performance with different ammonia‐water mixture ratios. An ammonia‐SOFC system was modeled in Cycle Tempo for detailed thermodynamic analysis. The heat from the electrochemical reaction in the SOFC and catalytic combustion in an afterburner is used in the struvite decomposition process. However, the generated heat is not sufficient to meet the heat demand of the struvite decomposition reactor. To improve the sustainability of the system in terms of heat demand, the system can be integrated into a heat pump assisted distillation tower, meanwhile, the ammonia concentration of the fuel stream increases. Increasing the ammonia concentration to 90 mol.% increases the energy and exergy efficiencies of the SOFC system. The net energy efficiency of the integrated system with a heat pump assisted distillation tower is 39%, based on the LHV of the ammonia‐water mixture.

Recovery of ammonia from wastewater through chemical precipitation

Chemical precipitation is a consolidated technique applied in wastewater treatment to remove and recover phosphorous and ammonium that remain in the effluent after the anaerobic digestion treatment. The precipitate is magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O), also known as struvite, and it is sold as a slow-release fertiliser. However, the value of struvite is quite low and has a limited market. Furthermore, it precipitates with heavy metals and other impurities that need to be removed to make the fertiliser commercially viable. This study looked at the thermal decomposition of struvite to recover added value products and recycle the magnesium for further precipitation. A kinetic study was carried out to understand the mechanism of decomposition and the formation of the different solid phases, which is fundamental for the design and optimisation of the technology. The thermogravimetric study confirmed that thermal decomposition is possible, but ammonia could not be completely released below 250 °C. The thermal analysis also led to the determination of the energy required for the decomposition, found to be 1.87 kJ g−1, which also includes the evaporation of water and ammonia. The kinetic study through the isoconversional method showed the presence of two major reactions, and the model-fitting approach identified the diffusion model as the best fit for the first reaction. The activation energy of the first reaction found with this method was 0.24 kJ g−1, comparable with the data obtained from the isoconversional method. The two-stage decomposition reactions were proposed, and the final calcination product was confirmed as magnesium pyrophosphate, which could be used in agriculture or dissolved in diluted mineral acids solution to separate the phosphate from the magnesium.

Thermal decomposition of struvite in water: qualitative and quantitative mineralogy analysis

ABSTRACT Struvite (MgNH4PO4·6H2O) is a potential fertilizer mineral that can be obtained from wastewaters. When the ambient temperature changes, struvite may decompose in water and other phosphate-bearing minerals form instead. The wet decomposition may include complex mineralization, as the struvite crystal structure releases both water molecules and ammonia. An in-situ x-ray measurement for the wet transformation of the struvite is needed to get insight into the mineral formed and into the influence of the water temperature on the decomposition/remineralization. In this study, the X-ray diffraction (XRD) sample holder containing struvite and water in a sealed condition was heated to temperatures of 55 to 120°C for 24 h. Later the still sealed sample holder was exposed to the X-ray beam with the Debye-Scherrer transmission technique, and the diffraction pattern was analyzed by the XRD Rietveld method. With increasing temperature (<100°C), struvite first dehydrated to dittmarite (MgNH4PO4·H2O). Moreover, a decomposition of struvite into an amorphous form of magnesium hydrogen phosphate has occurred as the XRD background increased dramatically and showed a structured profile with very broad intensity maxima. Furthermore, struvite transforms into dittmarite, newberyite, and bobierrite when the sample was heated above 100°C. The outcome of this work is expected to add knowledge on the instability of struvite, which may occur in the fields of the wastewater treatment and in the bio-mineralization in the urine of animals and humans.

Ammonium Removal from Landfill Leachate by Means of Multiple Recycling of Struvite Residues Obtained through Acid Decomposition

The treatment of landfill leachate, due to its great polluting load, is a very difficult task. In particular, the abatement of high ammonium concentrations represents one of the main issues. Among the available techniques, struvite precipitation is an effective method for the removal and recovery of NH4+ load. However, due to the lack of phosphorus and magnesium amounts, the struvite formation results in an expensive process in the leachate treatment. To overcome this issue, in the present work, we developed a simple and suitable method for ammonium removal by the multiple recycling of struvite decomposition residues. In this regard, a procedure for acid dissolution of struvite, produced by using industrial grade reagents, was initially defined. The effect of pH, temperature, and acid type was investigated. The experimental results proved the effectiveness of both hydrochloric and acetic acid, which allow a high and selective release of ammonium at T = 50 °C and pH = 5.5. The multiple reuse of decomposition products, combined with the supplementation of a small quantity of phosphorus and magnesium at molar ratios of n(N):n(Mg):n(P) = 1:0.05:0.05, guarantees stable NH4+ abatement of about 82%. The proposed process allows a cost saving of around to 74% and can be easily applied in industrial treatment plants.

Repeatedly using the decomposition product of struvite by ultrasound stripping to remove ammonia nitrogen from landfill leachate

In this study, the decomposition of struvite by ultrasound stripping and the recycle use of the decomposition product for the treatment of landfill leachate were investigated. The results indicated that when the decomposition of struvite by ultrasound stripping was performed at 55°C for 40min, the ammonium in the struvite could be almost completely eliminated from the solution system. The characterization analysis showed that magnesium phosphate and the dissolved phosphate ions were the main active derivatives. Approximately 90% of the total ammonia nitrogen (TAN) in landfill leachate can be removed by reusing the decomposition product at pH 9 for 60min. Repeated use of the struvite decomposition product revealed that the TAN removal efficiency decreased with an increase in the number of recycles. However, in the process of multiple recycling, about 90% of TAN removal could be maintained by supplementing a certain amount of the preformed struvite to the solution for every recycle. An economic analysis demonstrated that 79.3% of the treatment cost could be saved by the proposed process compared to the non-recycling process.

Synthesis and Characterisation of Struvite Family Crystals by An Aqueous Precipitation Method

Struvite (NH 4 MgPO 4 •6H 2 O) is a mineral often found as a scale deposit in an industrial process and piping. The common occurrence of struvite formation is a wide variety of environments. pH solution and environmental temperature are important parameters that control precipitation and subsequent decomposition of struvite. The study aims to characterise the struvite precipitated out the solution through chemical and mineralogical analysis. In this work, struvite solution was prepared by mixing NH 4 OH , MgCl 2 and H 3 PO 4 with the different purity grade (A and B) in the mol ratio of 1 : 1 : 1 in the stirred glass vessel tank with volume of 500 ml, and then stirred at 200 rpm for 70 minutes. Temperature of 3°C and an initial pH of 10 were selected. The precipitated deposit was dried at room temperature for 48 hours of being analyzed. Material characterization of the deposits was conducted using XRPD Rietveld method of qualitative and quantitative mineralogical phase analysis. XRF was employed for bulk chemical elemental analysis of the scale obtained. The sample A using analytical grade powder provided the major phases of struvite-(K) and struvite. In constrast, the major phase of newberyite and minor phases of lepidocrocite (FeOOH) and niter (KNO 3 ) was observed by following changes in the lowest purity of powder (Sample B). Analysis of the experimental data suggests a solution mediated transformation process as a possible mechanism of struvite transformation.

Recycling struvite pyrolysate obtained at negative pressure for ammonia nitrogen removal from landfill leachate

Struvite precipitation coupling low-cost materials and recycling was used to remove the total ammonia nitrogen (TAN) from landfill leachate in order to reduce the overall cost of precipitator. Struvite used for recycling was formed using a stabilizing agent (SA) as the precursor, which was formulated by using phosphorus acid and low-grade magnesium oxide (LG-MgO). Results showed that use of SA and LG-MgO for struvite precipitation can achieve TAN removal near that obtained by using pure chemicals. The results of struvite decomposition indicated that maintaining a negative pressure in struvite pyrogenation has a significant effect on the improvement of the ammonium release rate. When struvite pyrogenation was conducted at a vacuum degree of 0.04MPa and at a temperature of 120°C for 3h, the ammonium release rate was >90%. The obtained pyrolysate was recycled for the treatment of landfill leachate without the addition of other chemicals, and the TAN removal efficiency was comparable to that by struvite precipitation using fresh chemicals. When pyrolysate was used repeatedly by supplementing LG-MgO at the MgO:MgHPO4 molar ratio of 0.5:1 and by prolonging the stirring time to 2h, a TAN removal efficiency >68% could be maintained in the eight-cycle process. Economic analysis revealed that the proposed recycling process could reduce 86% of the cost of struvite precipitation using pure chemicals.

Recovery and removal of nutrients from swine wastewater by using a novel integrated reactor for struvite decomposition and recycling.

In the present study, struvite decomposition was performed by air stripping for ammonia release and a novel integrated reactor was designed for the simultaneous removal and recovery of total ammonia-nitrogen (TAN) and total orthophosphate (PT) from swine wastewater by internal struvite recycling. Decomposition of struvite by air stripping was found to be feasible. Without supplementation with additional magnesium and phosphate sources, the removal ratio of TAN from synthetic wastewater was maintained at >80% by recycling of the struvite decomposition product formed under optimal conditions, six times. Continuous operation of the integrated reactor indicated that approximately 91% TAN and 97% PT in the swine wastewater could be removed and recovered by the proposed recycling process with the supplementation of bittern. Economic evaluation of the proposed system showed that struvite precipitation cost can be saved by approximately 54% by adopting the proposed recycling process in comparison with no recycling method.

Study of Cd&amp;lt;sup&amp;gt;2+&amp;lt;/sup&amp;gt;, Al&amp;lt;sup&amp;gt;3+&amp;lt;/sup&amp;gt;, and SO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;2&amp;amp;minus;&amp;lt;/sup&amp;gt; Ions Influence on Struvite Precipitation from Synthetic Water by Dissolved CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Degasification Technique

The effect of cadmium, aluminum, and sulphate ions on struvite precipitation kinetics and morphology of solids obtained was investigated in this study. Thus, these ions were introduced as additives in solution where struvite precipitation was achieved. The main results obtained showed that the Cd2+ ions cause the probable co-formation, with struvite, of an amorphous phase observed from Cd2+ concentration of 10 mg/L; the addition of aluminum ions in the solution does not affect the nature of the crystalline phase, identified as struvite. However, these ions cause the formation of agglomerates of larger and larger as the concentration rises. Moreover, their increasing improved significantly the yield of phosphates removal; although the sulfate ions have no effect on the nature of the precipitated phase identified as struvite, independently of molar ratio studied, they affect the thermal decomposition of struvite. This latter is done in a single step by increasing the concentration of these ions for the SO42−/PO43− molar ratio of 8.

Chlorination decomposition of struvite and recycling of its product for the removal of ammonium-nitrogen from landfill leachate

Struvite (MgNH4PO4⋅6H2O) precipitation is a promising method for ammonium (NH4+) removal from the wastewater. However, the high cost incurred with the use of magnesium and phosphate sources hinders the successful application of this method. This paper presents a novel recycling technology of struvite that is based on the chlorination decomposition of struvite. The study results indicated that struvite can be effectively decomposed by sodium hypochlorite and that the solid/liquid ratio of struvite in solution did not affect the ammonium-nitrogen (NH4-N) decomposition efficiency of struvite. Through the analysis of the reaction process, the mechanism of struvite decomposition was proposed to be simultaneous dissolution and oxidation of struvite, and the main component of the decomposition product generated was determined to be newberyite, dissolved HPO42− and Mg2+, and magnesium phosphate. When the decomposition product was recycled, its pH had to be adjusted for high NH4-N removal. NH4-N of 92% could be removed from landfill leachate when the decomposition product solution pH before recycling was adjusted to 3 and the precipitation pH was maintained at 9. A five-cycle recycling process showed that recycling of struvite chlorination decomposition product was a highly efficient and sustainable method for the removal of NH4-N. An economic evaluation showed that the use of recycled struvite for the five-process cycles by the proposed process could save the cost of chemicals by approximately 34% as compared to the use of pure chemicals.

Minerals of the Wooltana Cave, Flinders Ranges, South Australia

Analysis of guano specimens from Wooltana cave, formerly occupied by ghost bats (Macroderma gigas), shows the principal mineral is whitlockite with seven other crystalline phases. These include dittmarite NH4MgPO4 ·H2O, biphosphammite (NH4K)H2PO4, syngenite K2Ca(SO4)2 ·H2O, görgeyite K2Ca5(SO4)6 ·H2O, brushite CaHPO4 ·2H2O, gypsum CaSO4 ·2H2O and whewellite CaC2O4 ·H2O. The mineralogy of the guano samples was determined by powder X-ray diffraction and field emission SEM and the phase analysis was quantified by Reitveld methods. Dittmarite is a very rare mineral and only reported from a small number of localities. It cannot be formed directly in caves as it is normally crystallised from boiling water. We propose that it is formed by decomposition of struvite, NH4MgPO4 ·6H2O, in the presence of ammonia arising from the fresh bat guano. The minerals dittmarite, struvite and newberyite, MgHPO4 ·3H2O, can transform between themselves in caves and in kidney stones (in vitro) according to the conditions. Two minerals, görgeyite, and whewellite, have not previously been reported from guano deposits. Gypsum and brushite are present in some samples and show up to 18% PO4 for SO4 in gypsum substitution and up to 18% SO4 for PO4 in brushite. Some pure end-member crystals were also identified. The whitlockite is also substituted by sulfate by up to 30% and averaging 10%. The cave walls are dolomite and a speleothem present shows calcite, magnesium calcite, gypsum and leonite, K2Mg(SO4)2 ·4H2O an unusual sulfate mineral. The extent and presence of the sulfates and of whewellite confirms that substantial ground water has entered the cave consistent with the known wetter past climate.

A kinetic study of struvite precipitation recycling technology with NaOH/Mg(OH)2 addition

Struvite precipitation recycling technology is received wide attention in removal ammonium and phosphate out of wastewater. While past study focused on process efficiency, and less on kinetics. The kinetic study is essential for the design and optimization in the application of struvite precipitation recycling technology. The kinetics of struvite with NaOH/Mg(OH)2 addition were studied by thermogravimetry analysis with three rates (5, 10, 20 °C/min), using Friedman method and Ozawa-Flynn-Wall method, respectively. Degradation process of struvite with NaOH/Mg(OH)2 addition was three steps. The stripping of ammonia from struvite was mainly occurred at the first step. In the first step, the activation energy was about 70 kJ/mol, which has gradually declined as the reaction progress. By model fitting studies, the proper mechanism function for struvite decomposition process with NaOH/Mg(OH)2 addition was revealed. The mechanism function was f(α)=α(α)-(1-α)(n), a Prout-Tompkins nth order (Bna) model.

Thermal decomposition of struvite and its phase transition

Intentional crystallization of struvite, before it forms and accumulates on wastewater treatment equipment, solves an important and costly wastewater treatment problem and on the other hand, provides an environmentally sound and renewable nutrient source to the agricultural industry. Struvite was synthesized in the laboratory; it was also produced as pellets in a pilot-scale, fluidized bed reactor, using real centrate resulting from an anaerobic digester. The thermal decomposition of both synthetic struvite and struvite pellets was studied. The decomposition of struvite was found to be dependent on the rate of heating. Through gradual loss of ammonia and water molecules, ultimately struvite was found to be transformed into amorphous magnesium hydrogen phosphate. When struvite was heated in excess water, it was partially transformed into bobierrite, through the gradual loss of ammonia. It was transformed into monohydrate, dittmarite by losing its five water molecules of crystallization, when boiled in excess water.

The decomposition of struvite: further evidence

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The decomposition of struvite

SummaryThe subaerial decomposition of struvite has been investigated at room temperature (21±2° C), from which it has been concluded that the decomposition product is newberyite. X-ray power patterns of newberyite, both from a diffractometer and Debye-Scherrer cameras, are given. Comparison of these patterns with other newberyite patterns suggest that the camera pattern is more reproducible; this may be due to grain orientation in the diffraetometer mounts.