Magnesium Potassium Phosphate Research Articles

Effects of graphene oxide on the properties and microstructures of the magnesium potassium phosphate cement paste

This paper presents the effect of graphene oxide (GO) on the properties and microstructures of the magnesium potassium phosphate cement (MKPC) paste with a lower water to solid ratio (w/s) of 0.15. The influence of GO on the workability, hydration degree, mechanical behavior and microstructures of the MKPC paste is systematically investigated. The experimental results showed that the addition of GO shorted the final setting time and decreased the workability of the MKPC paste, but the compressive and flexural strength of the MKPC paste were improved by a moderate addition of GO. It was clearly indicated that compared with the fresh MKPC paste, the addition of 0.05wt.% GO can improve the compressive and flexural strength of the MKPC paste by 6.8% and 8.3%, respectively. The improved mechanical strength is not only attributed to the excellent mechanical properties of GO itself, but also the higher hydration degree and lower porosity of the MKPC paste by the GO addition. The microstructures of the MKPC paste with GO addition of 0.05wt.% become much denser and better crystallization of the hydration products can be achieved, compared with the fresh MKPC paste. However, more GO addition 0.10wt.% has a negative effect on the crystallization of the hydration products and mechanical behavior of the MKPC paste. Finally, the FTIR spectra indicated that there was no chemical bonding between the hydration products of the MKPC paste and GO. It is concluded that GO, as a promising nanofiller, has a great potential for reinforcing the MKPC paste.

HIGH LEVEL WASTES IMMOBILIZATION IN CERAMIC AND HYDRATED PHOSPHATE MATRIX

The results of experimental research for obtaining of phosphate matrix materials: fluorapatite Ca10(PO4)6F2, sodium zirconium phosphate NaZr2(PO4)3 and potassium magnesium phosphate KMgPO4·6H2O were presented. The evolution of phase composition in their synthesis was investigated. The optimal parameters for obtaining monophasic phosphate matrix materials were found. Possibility of obtaining powders of calcium Ca10(PO4)6F2 and strontium-containing Ca9Sr(PO4)6F2 fluorapatites by both solid phase reaction method with subsequent heat treatment and chemical co-precipitation method from solutions of the initial components was investigated. Nanosized zirconium orthophosphate powders NaZr2(PO4)3 were synthesized by the sol-gel method. Hydrated phosphatic matrices KMgPO4·6H2O by a chemical reaction between MgO and KH2PO4 in water at a room temperature were obtained. The requirements for high-level waste matrix were presented. The suitability of the use of synthetic phosphate materials as a matrix for the immobilization of high level nuclear wastes was determined.

Solidification/stabilization of simulated cadmium-contaminated wastes with magnesium potassium phosphate cement

Magnesium potassium phosphate cement (MKPC) is an effective agent for solidification/stabilization (S/S) technology. To further explore the mechanism of the S/S by MKPC, two kinds of Cd including Cd(NO₃)2 solution (L-Cd) and municipal solid waste incineration fly ash (MSWI FA) adsorbed Cd (S-Cd), were used to compare the effects of the form of heavy metal on S/S. The results showed that all the MKPC pastes had a high unconfined compressive strength (UCS) above 11 MPa. For L-Cd pastes, Cd leaching concentration increased with the increase of Cd content, and decreased with the increase of curing time. With the percentage of MSWI FA below 20%, S-Cd pastes exhibited similar Cd leaching concentrations as those of L-Cd pastes, while when the content of MSWI FA come up to 30%, the Cd leaching concentration increased significantly. To meet the standard GB5085.3-2007, the highest addition of S-Cd was 30% MSWI FA (6% Cd contained), with the Cd leaching concentration of 0.817 mg/L. The S/S of L-Cd is mainly due to chemical fixation, and the hydration compound of Cd was NaCdPO₄, while the S/S of S-Cd is due to physical encapsulation, which is dependent on the pore/crack size and porosity of the MKPC pastes.

Experimental and computational investigation of magnesium phosphate cement mortar

For first time, an experimental and computational study has been conducted to investigate the properties of magnesium phosphate cement (MPC) mortar and its main hydration product struvite-K crystal that would account for the mechanical properties of these materials. Two types of MPC mortars, magnesium sodium phosphate cement (MNPC) and magnesium potassium phosphate cement (MKPC), were synthesized with magnesium to phosphate (M/P) ratio from 4 to 18 and water to solid ratio (w/s) from 0.16 to 0.2. Subsequently, the setting behavior, compressive strength and water resistance of MNPC and MKPC were investigated to study the influence of M/P and w/s ratios. An increase of M/P ratio can slow down the setting rate for both MPC mortar, and MNPC shows faster setting performance, as compared with MKPC. With increasing M/P ratio, the mechanical properties of MKPC mortar are gradually weakened, while the strength for MNPC mortar is first improved and then degrades, with the optimum value at M/P ratio of 9.5. Additionally, the saturated MPC mortars, immersed in water solution, are significantly weakened, showing poor water resistance. Micro-characterizations including X-ray diffraction and scanning electron microscopy of the MPC mortar reveal that MKPC mortars have good crystallization of struvite-K, with the morphology of plate packing at early hydration stage and the MNP hydrates show amorphous phase. Furthermore, molecular dynamics was conducted to study the structure, dynamics and mechanical properties of the main hydrated phase in MKPC cement, struvite-K crystal. The hydrolytic weakening effect of water molecules and failure mechanism have been unraveled that the H-bonds and KOs connections lose the chemical stability due to water attacking and tensile loading, which explains the severe failure of MPC mortar observed in the water resistant experiments.

Effect of the combination of fly ash and silica fume on water resistance of Magnesium–Potassium Phosphate Cement

The effect of the combination of fly ash and silica fume on the water resistance of Magnesium–Potassium Phosphate Cement (MKPC) was investigated, and the improvement mechanism was discussed based on the micro-analysis of XRD, FSEM and pore structure. The results indicate that, the physical effect of the combination of fly ash and silica fume on MKPC is dominated compared with the chemical effect because of the optimization of pore structure. The combination of fly ash and silica fume leads to higher density and later-age compressive strength of MKPCs compared to those without fly ash and silica fume under air curing and water curing, respectively. The strength retention ratios (namely water resistance) of MKPCs with the combination of fly ash and silica fume at 56days are found to be significantly higher than those without fly ash and silica fume.

Effects of municipal solid waste incineration fly ash on solidification/stabilization of Cd and Pb by magnesium potassium phosphate cement

Magnesium potassium phosphate cement (MKPC) is a novel agent for solidification/stabilization (S/S) of heavy metals. In this study, different ratios of municipal solid waste incineration fly ash (MSWI FA) were added to MKPC as an admixture to solidify/stabilize heavy metal in an attempt to reduce S/S cost while also disposing and reusing the MSWI FA. The effects of MSWI FA on different heavy metals, including Cd, Pb and a Cd–Pb mixture, were also investigated. The results showed that Cd leaching concentration increased gradually with increasing MSWI FA upon S/S of Cd or Cd–Pb mixtures, while Pb leaching concentration decreased, then increased for Pb and Cd–Pb mixtures. After curing for 90d, the compressive strength of all MKPC pastes decreased gradually with increasing MSWI FA. Generally, a percentage of MSWI FA below 40% is suitable for being used as an admixture of MKPC to S/S heavy metals, and less than 20% is suggested for being used as a component of construction material. As an admixture of MKPC, MSWI FA exhibited an obviously synergistic effect on S/S of Pb, while it had a lesser effect on S/S of Cd, primarily because of its great adsorption characteristics and chemical fixation of Pb.

In situ synchrotron powder diffraction study of the setting reaction kinetics of magnesium-potassium phosphate cements

This work reports a kinetic study of the formation of magnesium-potassium phosphate cements accomplished using in-situ synchrotron powder diffraction. The reaction: MgO+KH2PO4+5H2O→MgKPO4·6H2O was followed in situ in the attempt of contributing to explain the overall mechanism and assess the influence of periclase (MgO) grain size and calcination temperature (1400-1600°C) on the reaction kinetics. Numerical kinetic parameters for the setting reaction have been provided for the first time. The best fit to the kinetic data was obtained using a weighted nonlinear model fitting method with two kinetic equations, representing two consecutive, partially overlapping processes. MgO decomposition could be described by a first order (F1) model followed by a Jander diffusion (D3) controlled model. Crystallization of the product of reaction was modelled using an Avrami model (An) followed by a first order (F1) chemical reaction. A reaction mechanism accounting for such results has been proposed.

The resistance to high temperature of magnesia phosphate cement paste containing wollastonite

This paper aims to study the effect of wollastonite addition on the behavior of magnesium ammonium phosphate cement (MAPC) and magnesium potassium phosphate cement (MKPC) pastes exposed to different high temperatures. Different dosages of wollastonite were added to replace MgO powder in these two types of magnesia phosphate cements. The paste specimens were exposed to 105 °C for 24 h and to different temperatures of 200, 400, 600, 800 and 1000 °C for 3 h and then cooled to room temperature for different tests including mass loss, visual appearance, compressive strength, mineral composition and microstructure observation. The results show that the specimens containing 10 % wollastonite for both MAPC and MKPC mixtures presents the most improved high temperature resistance due to the excellent heat stability of wollastonite mineral and the refined microstructure. And the addition wollastonite has little influence on the hydration products of these two magnesia phosphate cements. Therefore, the incorporation of wollastonite is a potential method to improve the heat-resistance of MAPC or MKPC.

Evolution of phase assemblage of blended magnesium potassium phosphate cement binders at 200° and 1000°C

The fire performance of magnesium potassium phosphate cement (MKPC) binders blended with fly ash (FA) and ground granulated blast furnace slag (GBFS) was investigated up to 1000°C using X-ray diffraction, thermogravimetric analysis and SEM techniques. The FA/MKPC and GBFS/MKPC binders dehydrate above 200°C to form amorphous KMgPO4, concurrent with volumetric and mass changes. Above 1000°C, additional crystalline phases were formed and microstructural changes occurred, although no cracking or spalling of the samples was observed. These results indicate that FA/MKPC and GBFS/MKPC binders are expected to have satisfactory fire performance under the fire scenario conditions relevant to the operation of a UK or other geological disposal facility

Characterisation and development of fine porosity in magnesium potassium phosphate ceramics

Characterisation of porosity and microstructure in chemically-bonded ceramics was accomplished by small-angle neutron scattering. Microstructural parameters were also followed during the setting reaction and obtained kinetic curves were compared with results of XRD quantitative phase analysis up to 1 month. Results indicate that less reactive MgO yields a more compact microstructure, the same happens during the progress of the reaction. The reaction product forms from an amorphous precursor and its development was found to scale with the microstructural parameters. A change in reaction mechanism after 40min is suggested.

Simultaneous Recovery of Potassium, Chloride and Removal of COD from Landfill Leachate Concentrates Using a Combination of Cation-Exchange Membrane Electrolysis

Nanofiltration (NF) and reverse osmosis (RO) filtration system are widely used in landfill sites as polishing step for advanced treatment of landfill leachates. The membrane systems always generate large amount of concentrates containing high level of refractory organic compounds, potassium, chloride and other inorganics, which hardly be treated via conventional biological process. Thus, a proper disposal of these concentrates from or RO systems is critically important.The advanced oxidation processes (e.g, electrochemical oxidation, Fenton oxidation and ozone oxidation) are generally used in treatment of the concentrates. However, the potential resource such as K+and chloride in concentrates are not efficiently recycled but discharged to environment. In present study, we explore innovative and environmentally sustainable treatment processes, a combined cation-exchange membrane electrolysis (CEME)/magnesium potassium phosphate (MPP) crystallization process, for treating NF concentrate, which include (a) contaminant removal: organic pollutant and ammoniacal-nitrogen removal; (b) recycling and onsite reuse of chloride ions in the form of gaseous chlorine; (c) separation and beneficial recovery of potassium from NF concentrates. This study demonstrated that the proposed combined process can effectively remove 82%, 99%, 34%, 99% of organic matter, ammoniacal-nitrogen, total nitrogen, and chloride ions, respectively. And the recovered gaseous chlorine was reused on site as a decolorizing agent for synthetic dye (RhB) containing wastewater and complete decolorization was also achieved. The potassium ions were recovered via magnesium potassium phosphate crystallization . Additionly, about 53% of the potassium (from 2762 mg/L to 1389 mg/L) was removed via formation of magnesium potassium phosphate(MgKPO4·6H2O) precipitate. A combination of membrane electrolysis process is demonstrated to be an effective method for the convenient recycling of NF concentrates generated from a landfill plant. This combined process achieves effective removal of organic pollutants in the concentrates and complete removal of NH3-N via an active chlorine-mediated reaction. The combined process also simultaneously enables highly efficient recycling of chloride and potassium ions from NF concentrates as beneficial products (gaseous chlorine and MgKPO4·6H2O buffered fertilizer, respectively). Additionally, we have demonstrated that the recovered gaseous chlorine could be reused on site as a decolorizing agent for treating colored wastewater (i.e., RhB solution), and that complete decolorization could be achieved. The results indicates that recycling of NF concentrate via the combination process is feasible. Figure 1

마그네슘 인산칼륨 시멘트 모르타르의 배합요인이 초기재령 물성에 미치는 영향

마그네슘 인산칼륨 시멘트 모르타르의 배합요인이 초기재령 물성에 미치는 영향

Characterisation of magnesium potassium phosphate cements blended with fly ash and ground granulated blast furnace slag

Magnesium potassium phosphate cements (MKPCs), blended with 50wt.% fly ash (FA) or ground granulated blast furnace slag (GBFS) to reduce heat evolution, water demand and cost, were assessed using compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) spectroscopy on 25Mg, 27Al, 29Si, 31P and 39K nuclei. We present the first definitive evidence that dissolution of the glassy aluminosilicate phases of both FA and GBFS occurred under the pH conditions of MKPC. In addition to the main binder phase, struvite-K, an amorphous orthophosphate phase was detected in FA/MKPC and GBFS/MKPC systems. It was postulated that an aluminium phosphate phase was formed, however, no significant Al–O–P interactions were identified. High-field NMR analysis of the GBFS/MKPC system indicated the potential formation of a potassium-aluminosilicate phase. This study demonstrates the need for further research on these binders, as both FA and GBFS are generally regarded as inert fillers within MKPC.

The precipitation of magnesium potassium phosphate hexahydrate for P and K recovery from synthetic urine

Nutrients recovery from urine to close the nutrient loop is one of the most attractive benefits of source separation in wastewater management. The current study presents an investigation of the thermodynamic modeling of the recovery of P and K from synthetic urine via the precipitation of magnesium potassium phosphate hexahydrate (MPP). Experimental results show that maximum recovery efficiencies of P and K reached 99% and 33%, respectively, when the precipitation process was initiated only through adding dissolvable Mg compound source. pH level and molar ratio of Mg:P were key factors determining the nutrient recovery efficiencies. Precipitation equilibrium of MPP and magnesium sodium phosphate heptahydrate (MSP) was confirmed via precipitates analysis using a Scanning Electron Microscope/Energy Dispersive Spectrometer and an X-ray Diffractometer. Then, the standard solubility products of MPP and MSP in the synthetic urine were estimated to be 10−12.2 ± 0.0.253 and 10−11.6 ± 0.253, respectively. The thermodynamic model formulated on chemical software PHREEQC could well fit the experimental results via comparing the simulated and measured concentrations of K and P in equilibrium. Precipitation potentials of three struvite-type compounds were calculated through thermodynamic modeling. Magnesium ammonium phosphate hexahydrate (MAP) has a much higher tendency to precipitate than MPP and MSP in normal urine while MSP was the main inhibitor of MPP in ammonium-removed urine. To optimize the K recovery, ammonium should be removed prior as much as possible and an alternative alkaline compound should be explored for pH adjustment rather than NaOH.

Simultaneous solidification of potassium and phosphorus using rice straw charcoal and saturated phosphorus adsorbent

Phosphorus (P) ore is an expensive and limited resource that will be depleted in a few decades if the current global consumption rate continues. Japan, one of the most developed countries in the world, relies completely on imported phosphate rock for P. Potassium (K) ore, which is equally important for continuous development, is also becoming increasingly expensive. The recovery of P and K is therefore important for continuous and sustainable development. In this study, concentrated P (obtained from eluent) and K (obtained through alkali leaching of rice straw charcoal) were recovered as potassium magnesium phosphate (PMP) through the controlled addition of magnesium (Mg). A PMP crystal was produced when an equimolar (with respect to P) Mg solution was added to the leaching solution (rich in P and K) at a pH range of 11–12. Thus, the production of PMP in a crystalline form demonstrates the huge scope for the recycling of limited resources.

Recovery of potassium from landfill leachate concentrates using a combination of cation-exchange membrane electrolysis and magnesium potassium phosphate crystallization

Simultaneous removal of high levels of organic pollutants and recovery of nutrients from concentrates generated from the nanofiltration (NF) or reverse osmosis membrane separation process is a significant environmental challenge. In this study, a combined cation-exchange membrane electrolysis (CEME)/magnesium potassium phosphate crystallization process for the recycling of NF concentrates generated from treating landfill leachate was developed. These NF concentrates contained high levels of organics, ammoniacal-nitrogen, chloride as well as valuable potassium ions. The removal of these pollutants and feasibility of potassium recovery were evaluated. This study demonstrated that the proposed combined process can effectively remove 82%, 99%, 34%, 99% of organic matter, ammoniacal-nitrogen, total nitrogen, and chloride ions, respectively, while simultaneously allowing recovery of chloride and potassium ions from NF concentrates as beneficial products (gaseous chlorine and valuable magnesium potassium phosphate precipitates, a buffered fertilizer, respectively) and collection of a further electrolysis by-product (hydrogen). The recovered gaseous chlorine was reused on site as a decolorizing agent for synthetic dye containing wastewater and complete decolorization was achieved. The results indicate that recycling of NF concentrate via the CEME electrolysis/magnesium potassium phosphate crystallization process is feasible.

Influence of magnesia-to-phosphate molar ratio on microstructures, mechanical properties and thermal conductivity of magnesium potassium phosphate cement paste with large water-to-solid ratio

This paper describes the influence of the magnesia-to-phosphate (M/P) molar ratios ranging from 4 to 12, on the properties and microstructures of magnesium potassium phosphate cement (MKPC) pastes with a large water-to-solid ratio (w/s) of 0.50. The setting behavior, compressive strength, tensile bonding strength and thermal conductivity of the MKPC pastes, were investigated. The results show that an increase in the M/P ratio can slow down the setting reaction, and clearly degrade the mechanical strengths, but clearly improve the thermal conductivity of MKPC pastes. Furthermore, micro-characterizations including X-ray diffraction, scanning electron microscopy and thermogravimetric analysis, on the MKPC pastes reveal that a lower M/P ratio can facilitate better crystallization of the resultant magnesium potassium phosphate hexahydrate (MKP) and a denser microstructure. Moreover, strong linear correlations are found between the mechanical strengths and the MKP-to-space ratio, and between thermal conductivity and the volume ratio of the unreacted magnesia to the MKP.

Curing Behavior and Structure of Magnesium Phosphate Chemically Bonded Ceramics with Different MgO to KH2PO4 Ratios

Magnesium phosphate chemically bonded ceramics attracted much attention because of its good biocompatibility. In this work, curing behavior and microstructure of magnesium phosphate chemically bonded ceramics with different MgO to KH2PO4 ratios were investigated. The results showed that the setting time decreased and the maximum temperature during the solidifying process increased as the increase of MgO to KH2PO4 ratio. Phase compositions were different for those samples fabricated with different MgO to KH2PO4 ratios. KH2PO4, MgO, and hydrated product existed in the sample with lower MgO to KH2PO4 ratio because of the incomplete reaction, and numerous acicular polycrystals were found. There were only MgO and hydrated product existed with the higher MgO to KH2PO4 ratio. Besides, a gelatinous structure with lots of cracks was also found. Clearly, the properties of magnesium potassium phosphate chemically bonded ceramics could be controlled by changing the MgO to KH2PO4 ratio. It is better to fabricate magnesium phosphate chemically bonded ceramics with optimal structure and properties suitable for biomedical applications in range of MgO to KH2PO4 ratio from 3:1 to 4:1 in this preparating conditions.

Effects of water content, magnesia-to-phosphate molar ratio and age on pore structure, strength and permeability of magnesium potassium phosphate cement paste

In this study, the pore structure of magnesium potassium phosphate cement paste is investigated using mercury intrusion porosimetry. Several mix proportions, obtained by changing the magnesia-to-phosphate molar ratio (M/P) and the water-to-cement mass ratio (W/C) of the material, are involved. It is found that lower W/C and longer material age make the porosity lower and the pore structure finer. When the W/C is kept constant, both porosity and critical pore diameter are not monotonic functions of M/P, but the M/P of 6 gives the lowest porosity and the smallest critical pore diameter. Also, the M/P of 6 shows the highest compressive strength and the lowest intrinsic permeability. Based on the experimental results, empirical models describing the relations between the properties and pore structure parameters (porosity ϕ and critical pore diameter dc) of MKPC paste are developed. The compressive strength is inversely proportional to ϕ, and the intrinsic permeability is directly proportional to dc2ϕ.

Magnesium potassium phosphate cement paste: Degree of reaction, porosity and pore structure

Although magnesia–phosphate cements have been studied and applied in several fields for many years, the theoretical background on this kind of chemically bonded ceramics has not been sufficiently well established for the quantitative prediction of material properties. In this study, the stoichiometric factors of the chemical reaction in magnesium potassium phosphate cement (MKPC) paste are analyzed, and the degree of reaction of this cement is defined. Based on the stoichiometric factors and the degree of reaction, the porosity of MKPC paste, which is essential for predictions of both the mechanical and transport properties, is calculated. In addition, the pore structure is simulated by a newly developed computer model. The calculated porosities and the simulated pore structures are both found to be consistent with the results measured by mercury intrusion porosimetry (MIP).