Here we report that the presence of MgCO_(3) stimulates the extracellular polymeric substance (EPS) secretion of Microcystis Aeruginosa (M. Aeruginosa). This stimulation led to a significant reduction in the total con...Here we report that the presence of MgCO_(3) stimulates the extracellular polymeric substance (EPS) secretion of Microcystis Aeruginosa (M. Aeruginosa). This stimulation led to a significant reduction in the total concentration of NH_(4)^(+)‒N by more than 86%, and effective recovery of PO_(4)^(3-)‒P within three days from concentrated wastewater (WW), although the secreted EPS inhibited the conversion of MgCO_(3) to specific crystal forms (MgNH4PO4.6H2O or MgHPO4.7H2O). Moreover, with an increase in PO_(4)^(3-) concentration in WW, these crystals appeared, thus the removal of NH_(4)^(+)‒N and PO_(4)^(3-)‒P nutrients can be attributed to the combined effect of M. Aeruginosa and MgCO_(3). We used Surface-Enhanced Raman Spectroscopy (SERS) combined with X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (FESEM-EDS), and X-ray Photoelectron Spectroscopy (XPS) to investigate the mechanism for competitive interactions between M. Aeruginosa and MgCO_(3) in removing NH_(4)^(+)‒N and PO_(4)^(3-)‒P. We identified that the bound EPS accumulated amorphous Mg–P–O dense particles on M. Aeruginosa, while soluble EPS, containing –COOH groups of humic-like substances decreased the pH of the solution and coordinated with Mg^(2+) ions. Therefore, both secreted bound and soluble EPS play a vital role in hindering the transformation of Mg^(2+) ions or MgCO_(3) to MgNH4PO4.6H2O or MgHPO4.7H2O crystals within WW, and they enhanced M. Aeruginosa 's ability in absorbing nutrients of NH_(4)^(+)‒N and PO_(4)^(3-)‒P. This mechanism plays a crucial role in the efficient recovery of NH_(4)^(+)‒N and PO_(4)^(3-)‒P from concentrated wastewater sources such as aerobically or anaerobically digested effluent from various sources like agriculture, livestock, and domestic wastewaters.展开更多
The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO_(3)were investigated and then a refining technique was developed.Simultaneously,the corresponding mechanisms were discussed...The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO_(3)were investigated and then a refining technique was developed.Simultaneously,the corresponding mechanisms were discussed.The results indicate that increasing addition temperature of MgCO_(3)or pouring temperature is beneficial for obtaining fine grains.There is an optimal addition amount of 1.2%at the addition temperature of 790°C.Prolonging holding time at 790°C will increase grain size.The grain refining technique that 1.2%MgCO_(3)is added at 790°C followed by holding for 10 min and pouring can decrease the grain size from 348μm of the un-refined alloy to 69μm.The nucleation substrates are actually the Al4C3 particles formed from reactions between the MgCO_(3)and alloying elements in the melt.Besides the heterogeneous nucleation regime,growth restriction of the Al4C3 particles agglomerated at growing front is the other mechanism.展开更多
The large and uneven grain size of anhydrous magnesium carbonate (MgCO_(3)) seriously restricts its application ranges and performances. In this study, we proposed a controllable and cost-effective strategy to synthes...The large and uneven grain size of anhydrous magnesium carbonate (MgCO_(3)) seriously restricts its application ranges and performances. In this study, we proposed a controllable and cost-effective strategy to synthesize uniform small-sized MgCO_(3) from Mg^(2+) concentrated seawater brine in the absence of crystal modifiers. In this process, solid NaOH was directly added to Mg^(2+) concentrated seawater brine to completely and rapidly convert Mg^(2+) to magnesium hydroxide (Mg(OH)_(2)) nanoparticles. These nanoparticles are redispersed in water to form the colloidal system, where Mg(OH)_(2) nanoparticles hydrothermally reacts with urea to obtain uniform small-sized MgCO_(3) particles. The influence of reaction temperature, reaction time, and the molar ratio of magnesium ions to urea on the synthesis of MgCO_(3) is systematically investigated. In the highly-dispersed and stable colloidal system, Mg(OH)2 nanoparticles could exert an effective and sustained retarding effect on the hydrolysis rate of urea by attracting free water, resulting in the controllable release of NH_(4)^(+), CO_(3)^(2−), and Mg^(2+). This study presents a simple route to realize the controllable synthesis of uniform small-sized MgCO_(3) particles, and demonstrates the feasibility of using MgCO_(3) as an ideal filler for enhancing the performance of polymers as well as an ideal precursor for high-purity MgO production.展开更多
The homogeneous and controllable morphology of anhydrous magnesium carbonate(MgCO_(3))particles with excellent properties is difficult to obtain because of a variety of synthetic factors.The effect of succinic acid as...The homogeneous and controllable morphology of anhydrous magnesium carbonate(MgCO_(3))particles with excellent properties is difficult to obtain because of a variety of synthetic factors.The effect of succinic acid as a crystal modifier on the particle morphology transformation of anhydrous MgCO_(3)was investigated by the hydrothermal method.The effect of the addition of succinic acid on the particles was similar to that of temperature change.The morphology of particles with a folded diamond-like shape was gradually uniform,and the particle size was between 3.3 and 7.5μm.Anhydrous MgCO_(3)particles prepared at pH 9 could easily agglomerate,and the average particle size increased from diamond-like to cube-like as the reaction time increased.The interaction between succinic acid and magnesium ions at different concentrations was the main factor responsible for the morphological changes.The pH,temperature,and time affected the molecular motion rate and crystal growth.展开更多
基金supported by Cultivating Fund Project of Hubei Hongshan Laboratory(2022hspy002).
文摘Here we report that the presence of MgCO_(3) stimulates the extracellular polymeric substance (EPS) secretion of Microcystis Aeruginosa (M. Aeruginosa). This stimulation led to a significant reduction in the total concentration of NH_(4)^(+)‒N by more than 86%, and effective recovery of PO_(4)^(3-)‒P within three days from concentrated wastewater (WW), although the secreted EPS inhibited the conversion of MgCO_(3) to specific crystal forms (MgNH4PO4.6H2O or MgHPO4.7H2O). Moreover, with an increase in PO_(4)^(3-) concentration in WW, these crystals appeared, thus the removal of NH_(4)^(+)‒N and PO_(4)^(3-)‒P nutrients can be attributed to the combined effect of M. Aeruginosa and MgCO_(3). We used Surface-Enhanced Raman Spectroscopy (SERS) combined with X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (FESEM-EDS), and X-ray Photoelectron Spectroscopy (XPS) to investigate the mechanism for competitive interactions between M. Aeruginosa and MgCO_(3) in removing NH_(4)^(+)‒N and PO_(4)^(3-)‒P. We identified that the bound EPS accumulated amorphous Mg–P–O dense particles on M. Aeruginosa, while soluble EPS, containing –COOH groups of humic-like substances decreased the pH of the solution and coordinated with Mg^(2+) ions. Therefore, both secreted bound and soluble EPS play a vital role in hindering the transformation of Mg^(2+) ions or MgCO_(3) to MgNH4PO4.6H2O or MgHPO4.7H2O crystals within WW, and they enhanced M. Aeruginosa 's ability in absorbing nutrients of NH_(4)^(+)‒N and PO_(4)^(3-)‒P. This mechanism plays a crucial role in the efficient recovery of NH_(4)^(+)‒N and PO_(4)^(3-)‒P from concentrated wastewater sources such as aerobically or anaerobically digested effluent from various sources like agriculture, livestock, and domestic wastewaters.
基金Project(G2010CB635106)supported by the National Basic Research Program of China+1 种基金Project(NCET-10-0023)supported by the Program for New Century Excellent Talents in University of China
文摘The effects of grain refining parameters on microstructure of AM60B magnesium alloy with MgCO_(3)were investigated and then a refining technique was developed.Simultaneously,the corresponding mechanisms were discussed.The results indicate that increasing addition temperature of MgCO_(3)or pouring temperature is beneficial for obtaining fine grains.There is an optimal addition amount of 1.2%at the addition temperature of 790°C.Prolonging holding time at 790°C will increase grain size.The grain refining technique that 1.2%MgCO_(3)is added at 790°C followed by holding for 10 min and pouring can decrease the grain size from 348μm of the un-refined alloy to 69μm.The nucleation substrates are actually the Al4C3 particles formed from reactions between the MgCO_(3)and alloying elements in the melt.Besides the heterogeneous nucleation regime,growth restriction of the Al4C3 particles agglomerated at growing front is the other mechanism.
基金We are grateful for the financial support from the National Natural Science Foundation of China(grant Nos.22478095 and 22008049)Key Research and Development Project of Hebei Province,China(grant No.22374101D).
文摘The large and uneven grain size of anhydrous magnesium carbonate (MgCO_(3)) seriously restricts its application ranges and performances. In this study, we proposed a controllable and cost-effective strategy to synthesize uniform small-sized MgCO_(3) from Mg^(2+) concentrated seawater brine in the absence of crystal modifiers. In this process, solid NaOH was directly added to Mg^(2+) concentrated seawater brine to completely and rapidly convert Mg^(2+) to magnesium hydroxide (Mg(OH)_(2)) nanoparticles. These nanoparticles are redispersed in water to form the colloidal system, where Mg(OH)_(2) nanoparticles hydrothermally reacts with urea to obtain uniform small-sized MgCO_(3) particles. The influence of reaction temperature, reaction time, and the molar ratio of magnesium ions to urea on the synthesis of MgCO_(3) is systematically investigated. In the highly-dispersed and stable colloidal system, Mg(OH)2 nanoparticles could exert an effective and sustained retarding effect on the hydrolysis rate of urea by attracting free water, resulting in the controllable release of NH_(4)^(+), CO_(3)^(2−), and Mg^(2+). This study presents a simple route to realize the controllable synthesis of uniform small-sized MgCO_(3) particles, and demonstrates the feasibility of using MgCO_(3) as an ideal filler for enhancing the performance of polymers as well as an ideal precursor for high-purity MgO production.
基金the National Natural Science Foundation of China(grant No.U22A20434)the Foundation from Qinghai Science and Technology Department(grant No.2022-ZJ-706).
文摘The homogeneous and controllable morphology of anhydrous magnesium carbonate(MgCO_(3))particles with excellent properties is difficult to obtain because of a variety of synthetic factors.The effect of succinic acid as a crystal modifier on the particle morphology transformation of anhydrous MgCO_(3)was investigated by the hydrothermal method.The effect of the addition of succinic acid on the particles was similar to that of temperature change.The morphology of particles with a folded diamond-like shape was gradually uniform,and the particle size was between 3.3 and 7.5μm.Anhydrous MgCO_(3)particles prepared at pH 9 could easily agglomerate,and the average particle size increased from diamond-like to cube-like as the reaction time increased.The interaction between succinic acid and magnesium ions at different concentrations was the main factor responsible for the morphological changes.The pH,temperature,and time affected the molecular motion rate and crystal growth.
