Separation of manganese from calcium and magnesium in sulfate solutions via carbonate precipitation

The separation of manganese from sulfate solutions containing 14.59 g/L Mn2+, 1.89 g/L Mg2+ and 1.54 g/L Ca2+ was preformed successfully by carbonate precipitation. The results of thermodynamic analysis and tests indicate that carbonate precipitation holds better selectivity for manganese over magnesium than hydroxide precipitation and the feeding method is the most critical factor for minimizing the co-precipitation of calcium and magnesium. Furthermore, with adding MnSO4 solution to NH4HCO3 solution, the effects of the initial NH4HCO3 concentration, NH4HCO3 amount, solution pH value, reaction temperature and time on carbonate precipitation were evaluated and the optimum precipitation conditions were obtained. Under the optimum conditions, the precipitation rates of Mn2+, Ca2+ and Mg2+ are 99.75%, 5.62% and 1.43%, respectively. Moreover, the prepared manganese carbonate was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX). The results demonstrate that the product can be indexed to the rhombohedral structure of MnCO3.

Experimental study on mitigating wind erosion of calcareous desert sand using spray method for microbially induced calcium carbonate precipitation

Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e.allergies and respiratory diseases, due to the presence of harmful contaminants, bacteria, and pollens.The present study evaluates the feasibility of microbially induced calcium carbonate precipitation(MICP)technique to mitigate wind-induced erosion of calcareous desert sand(Thar desert of Rajasthan province in India). The temperature during biotreatment was kept at 36℃ to stimulate the average temperature of the Thar desert. The spray method was used for bioaugmentation of Sporosarcina(S.) pasteurii and further treatment using chemical solutions. The chemical solution of 0.25 pore volume was sprayed continuously up to 5 d, 10 d, 15 d, and 20 d, using two different concentration ratios of urea and calcium chloride dihydrate viz 2:1 and 1:1. The biotreated samples were subjected to erosion testing(in the wind tunnel) at different wind speeds of 10 m/s, 20 m/s, and 30 m/s. The unconfined compressive strength of the biocemented crust was measured using a pocket penetrometer. The variation in calcite precipitation and microstructure(including the presence of crystalline minerals) of untreated as well as biotreated sand samples were determined through calcimeter, scanning electron microscope(SEM), and energydispersive X-ray spectroscope(EDX). The results demonstrated that the erosion of untreated sand increases with an increase in wind speeds. When compared to untreated sand, a lower erosion was observed in all biocemented sand samples, irrespective of treatment condition and wind speed. It was observed that the sample treated with 1:1 cementation solution for up to 5 d, was found to effectively resist erosion at a wind speed of 10 m/s. Moreover, a significant erosion resistance was ascertained in15 d and 20 d treated samples at higher wind speeds. The calcite content percentage, thickness of crust,bulk density, and surface strength of biocemented sand were enhanced with the increase in treatment duration. The 1:1 concentration ratio of cementation solution was found effective in improving crust thickness and surface strength as compared to 2:1 concentration ratio of cementation solution. The calcite crystals formation was observed in SEM analysis and calcium peaks were observed in EDX analysis for biotreated sand.

Field trial on use of soybean crude extract for carbonate precipitation and wind erosion control of sandy soil

Wind erosion is a major cause of land desertification and sandstorm formation in arid and semi-arid areas.The objective of this study was to evaluate the potential of soybeans crude extract induced calcium carbonate precipitation(SICP)on reducing wind erosion risk of sandy soil.Field tests were carried out in Ulan Buh Desert,Ningxia Hui Autonomous Region,China.Results showed that the SICP method could significantly enhance the surface strength and wind erosion resistance of the topsoil.The optimal cementation solution(urea-CaCl2)concentration and spraying volume,according to experiments conducted on sandy land,were 0.2 mol/L and 4 L/m^2,respectively.Under this condition,the CaCO3 content was approximately 0.45%,the surface strength of sandy soil could reach 306.2 kPa,and the depth of wind erosion was approximately zero,after 30 d completion of SICP treatment.Soil surface strength declined with the increase of time,and long-term sand fixation effects of SICP treatment varied depending on topography.Whereas wind erosion in the top area of the windward slope was remarkable,sandy soils on the bottom area of the windward slope still maintained a relatively high level of surface strength and a low degree of wind erosion 12 month after SICP treatment.Scanning electron microscopy(SEM)tests with energy dispersive X-ray(EDX)confirmed the precipitation of CaCO3 and its bridge effect.These findings suggested that the SICP method is a promising candidate to protect sandy soil from wind erosion in desert areas.

Preparation and Characterization of Three-dimensional Chrysanthemun Flower-like Calcium Carbonate

Calcium carbonate with three-dimensional chrysanthemun flower-like structure was successfully prepared from calcium chloride and sodium carbonate ethanol/water mixed solution by a simple precipitation method,using trisodium citrate as crystal modifier.The experimental results show that the three-dimensional structure of chrysanthemun flower-like calcium carbonate is built up with several symmetrical micrometer multi-layer petals arranged around the multi-layer pancake-liked center,and the micrometer center and petals are assemblied by a large number of nanometer spherical particles with size 10-20 nm.It is found that the amount of trisodium citrate,the ethanol volume content has an important influence on the formation of this morphology.A possible mechanism is proposed to explain the formation of three-dimensional chrysanthemun flower-like calcium carbonate according the results.Scanning electron microscopy（SEM）,X-ray powder diffraction（XRD）,flourier transform infrared spectroscopy（FT-IR）,thermogravimety analysis（TG）,transmission electron microscopy（TEM） equipped with energy-dispersive X-ray（EDX）,and selected area electron diffraction（SAED） were used to characterize the crystals.

Efficacy of Ca/ZSM-5 zeolites derived from precipitated calcium carbonate in the methanol-to-olefin process

In the context of heightened environmental consciousness and the growing demand for light olefins,this study explores the promising future prospects for their sustainable production from renewable resources.Light olefins(especially propylene)are a pivotal constituent of the petrochemical industry,and their demand is poised for steady growth driven by various sectors(e.g.,electric mobility,consumer goods and packaging industries),which should not rely solely on traditional petroleum-led routes.Therefore,sustainable pathways,such as the methanol-to-olefin(MTO)process catalyzed by zeolites,are gaining attention.Intending to couple the future olefin demands with the concept of a"methanol economy",this study investigates the synthesis of hierarchical Ca/ZSM-5 zeolites using a cost-effective approach involving Precipitated Calcium Carbonate(PCC)as a hard template,leading to superior catalytic performance.Comprehensive characterization techniques are employed to elucidate the cata-lyst's properties,highlighting the dual importance of mesoporosity and calcium species in optimizing its per-formance.Operando spectroscopy provides in-depth insights into its enhanced anti-coking characteristics.This research contributes to expanding the catalyst toolkit for zeolite-catalyzed MTO processes,focusing on propylene production,thereby addressing the increasing demand for light olefins while promoting sustainability and circular economy principles.

Characterization of calcium deposition induced by Synechocystis sp. PCC6803 in BG11 culture medium

Calcium carbonate （CaCO3） crystals in their preferred orientation were obtained in BG11 culture media inoculated with Synechocystis sp. PCC6803 （inoculated BG11）. In this study, the features of calcium carbonate deposition were investigated. Inoculated BGll in different calcium ion concentrations was used for the experimental group, while the BGll culture medium was used for the control group. The surface morphologies of the calcium carbonate deposits in the experimental and control groups were determined by scanning and transmission electron microscopy. The deposits were analyzed by electronic probe micro-analysis, Fourier transform infrared spectrum, X-ray diffraction, thermal gravimetric analysis and differential scanning calorimetry. The results show that the surfaces of the crystals in the experimental group were hexahedral in a scaly pattern. The particle sizes were micrometer-sized and larger than those in the control group. The deposits of the control group contained calcium （Ca）, carbon （C）, oxygen （O）, phosphorus （P）, iron （Fe）, copper （Cu）, zinc （Zn）, and other elements. The deposits in the experimental group contained Ca, C, and O only. The deposits of both groups contained calcite. The thermal decomposition temperature of the deposits in the control group was lower than those in the experimental group. It showed that the CaCO3 deposits of the experimental group had higher thermal stability than those of the control group. This may be due to the secondary metabolites produced by the algae cells, which affect the carbonate crystal structure and result in a close-packed structure. The algae cells that remained after thermal weight loss were heavier in higher calcium concentrations in BGll culture media. There may be more calcium- containing crystals inside and outside of these cells. These results shall be beneficial for understanding the formation mechanism of carbonate minerals.

An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater and saline water

Inorganic calcium carbonate precipitation from natural seawater and salinewater at various pH values was carried out experimentally. The results show the clear positiverelationships between boron concentration and δ^(11)B of inorganic calcium carbonate with the pH ofnatural seawater and saline water. However, the variations of boron isotopic fractionation betweeninorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis thatB(OH)_4^- is the dominant species incorporated into the biogenic calcite structure. The isotopicfractionation factors a between synthetic calcium carbonate precipitate and parent solutionsincrease systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawaterand from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopicfractionation factor of larger than 1 in synthetic calcium carbonate precipitated fromseawater/saline water at higher pH is observed, which implies that a substantial amount of theisotopically heavier B(OH)_3 species must be incorporated preferentially into synthetic inorganiccarbonate. The results propose that the incorporation of B(OH)_3 is attributed to the formation ofMg(OH)_2 at higher pH of calcifying microenvironment during the synthetic calcium carbonateprecipitation. The preliminary experiment of Mg(OH)_2 precipitated from artificial seawater showsthat heavier ^(11)B is enriched in Mg(OH)_2 precipitation, which suggests that isotopically heavierB(OH)_3 species incorporated preferentially into Mg(OH)_2 precipitation. This result cannot beapplied to explain the boron isotopic fractionation of marine bio-carbonate because of thepossibility that the unusual environment in this study appears in formation of marine bio-carbonateis infinitesimal. We, however, must pay more attention to this phenomenon observed in this study,which accidentally appears in especially natural environment.

沉淀碳酸钙(PCC)的发展及应用

简述碳酸钙的分类、用途、工业现状、国内外在碳酸钙多相合成体系流变学及转递行为、碳酸钙形成机理和形态控制技术以及结晶生长成核理论的研究成果 ,并讨论了碳酸钙粉末表面处理的方法、机理。

磷酸及磷酸／辅助剂对PCC的溶解抑制作用

将磷酸及磷酸/辅助剂加入至沉淀碳酸钙(PCC)填料悬浮液中,对填料进行改性处理,探讨了改性剂对PCC的溶解抑制作用。实验结果表明,改性剂磷酸、磷酸/六偏磷酸钠、磷酸/乙二胺四乙酸二钠、磷酸/硫酸铝及磷酸/氯化铝均具有一定的溶解抑制作用,改性填料悬浮液的pH值均有所下降;稀释改性填料悬浮液,悬浮液pH值随稀释倍数的增加而不断上升,其中磷酸/六偏磷酸钠改性填料悬浮液的pH值最低;改性后的填料在pH值为4.50和5.00的稀盐酸溶液、4.50和5.00的硫酸铝溶液、5.85的蒸馏水及7.26的自来水中的溶解性均有所降低,其中磷酸/六偏磷酸钠的溶解抑制作用最为显著,磷酸及六偏磷酸钠的较适宜用量分别为4%和1%。

PCC对涂料流变性和涂布纸性能的影响

研究了PCC对涂料流变特性、涂布纸性能的影响,比较了PCC和高岭土对涂布纸性能的影响。研究发现,随着PCC在涂料配比中用量的增加,涂料低剪切黏度降低,导致涂料保水性变差,不利于涂料固含量增加;涂料高剪切黏度增加,会对涂布机的运行性能产生负面影响。但是,PCC有利于增加L*值和a*值,降低b*值,能提高涂布纸的白度和不透明度,减少荧光增白剂用量。PCC有利于增加涂层表面强度。随着PCC用量的增加,油墨吸收性增加。与高岭土相比,在达到相同成纸表面强度的条件下,能降低胶黏剂用量。

介质黏度对PCC分散体系流变行为的影响

在AR2000ex型流变仪上对沉淀碳酸钙(Precipitated calcium carbonate,PCC)在PEG(聚乙二醇)悬浮体系进行稳态剪切流变实验。通过2种方法来改变分散体系黏度:1)以PEG200(相对分子质量为200)为连续相,分散体系以10℃为间隔从10℃上升至50℃;2)在30℃用相同的聚合物3种不同相对分子质量的PEG(PEG200、PEG400和PEG600)。结果表明随着温度升高,PCC/PEG200分散体系的临界剪切速率越来越大。在剪切增稠区内流动指数N随温度升高而降低,稠度系数K随着温度升高而升高。临界剪切速率以及临界剪切黏度与温度严格满足Arrhenius关系:η=A exp[Ea/(RT)]。研究发现随温度的变化临界剪切应力不变。随着PEG的相对分子质量增加,分散体系的黏度增加,临界剪切增稠速率减小。PCC粉末的分形结构以及聚集体的形貌使得体系的相对黏度远大于硬球体系的相对黏度。

硅酸钠基改性体系对PCC的溶解抑制作用

将硅酸钠基改性体系引入至PCC填料悬浮液中,制得改性填料悬浮液,对各种改性体系的溶解抑制作用进行了比较与分析。实验结果表明,硅酸钠/硫酸铝、硅酸钠/氯化铝、硅酸钠/磷酸、硅酸钠/磷酸/六偏磷酸钠及硅酸钠/磷酸/聚丙烯酸钠均具有一定的溶解抑制作用,改性后的填料悬浮液的pH值均有所下降;对改性填料悬浮液进行稀释,悬浮液pH值随稀释倍数的增加而上升;改性后的填料在pH值为4.50和5.00的稀盐酸溶液、pH值为4.50和5.00的硫酸铝溶液、pH值为5.85的蒸馏水及pH值为7.26的自来水中的溶解性均有所降低,其中硅酸钠/硫酸铝及硅酸钠/氯化铝的溶解抑制作用较弱,硅酸钠/磷酸、硅酸钠/磷酸/六偏磷酸钠及硅酸钠/磷酸/聚丙烯酸钠的溶解抑制作用较强;对于各种溶液体系而言,硅酸钠/磷酸/六偏磷酸钠均具有较为有效的溶解抑制作用。

用海藻酸钠改性PCC提高纸张施胶度和抗张强度

采用海藻酸钠对沉淀碳酸钙(PCC)进行改性,研究了改性PCC填料加填纸张的施胶度和抗张强度。结果表明,海藻酸钠改性PCC的最佳改性工艺条件为:海藻酸钠与PCC质量比为1∶140,改性时间为5 min,硫酸铝的用量(相对于PCC)为2%,在此最佳实验条件下获得的海藻酸钠改性PCC可以显著地提高其加填纸张的施胶度和抗张强度。

Shear-thickening rheological response of PCC/PEG suspensions

The steady and dynamic rheological behaviors of precipitated calcium carbonate (PCC) suspension in polyethylene glycol (PEG) were investigated on a TA AR2000ex rheometer. Under steady shear consistency index K and flow exponent N of suspensions with different volume fractions were determined. The shear-thinning and the discontinuous shear-thickening behavior were observed at different constant frequencies from 10 to 100 rad/s. The relationship between the complex viscosity and the constant frequency were determined. As the volume fraction increases,flow exponent N shows a rapid increase,and it increases dramatically when the discontinuous shear-thickening takes place,while consistency index K decreases. Dynamic oscillatory shear experiments were conducted at constant strain amplitude and constant frequency,respectively. For the frequency sweep,the system shows viscous property in entire range of the frequency investigated,and the complex viscosity shows discontinuous jump at a critical frequency of 10 rad/s. For the strain sweep,on the other hand,at low strain the elastic modulus is strongly dependent on the strain,and the viscous modulus is independent of the strain. But at the critical strain point both of the moduli show an abrupt jump and the system transits from elastic to viscous at a strain of 0.1.

Efects of amine, amine salt and amide on the behaviour of carbon dioxide absorption into calcium hydroxide suspension to precipitate calcium carbonate

The amount of carbon dioxide （CO2） absorption and calcium ion （Ca^2＋） concentration besides the pH of aqueous solution were observed during the COz absorption to precipitate calcium carbonate （CaCO3） from calcium hydroxide （Ca（OH）2）. A reaction rate-limiting effect of an amount of CO2 absorption without any organic additives in the early stage of the precipitation was observed, which was attributed to an interruption effect of bicarbonate ion （HCO3） on the precipitation of CaCO3. The improvement for the reaction rate was achieved not only by amine additives but also by neutral additives such as ε-caprolactam or amine salt. When the hexamethylene diamine was dissolved in the solution, successive change of crystal forms of CaCO3 aragonite to calcite in aqueous suspensions, confirmed by Ca^2＋ concentration change and X-ray diffraction, was concluded that a local environment around the amine group in aqueous solution and an interaction of the diamine with precipitated CaCO3 particles were important factors for these reactions.

Effect of wastewater composition on the calcium carbonate precipitation in upflow anaerobic sludge blanket reactors

Calcium carbonate often precipitates in anaerobic reactors treating wastewater with high calcium content.The aim of this paper is to study the effect of wastewater composition on calcium carbonate precipitation in upflow anaerobic sludge blanket(UASB)reactors.Two laboratory-scale UASB reactors were operated with calcium-containing influents using acetate and carbohydrate as substrate,respectively.There was an obvious accumulation of inorganic precipitate observed in the biogranules.Observations via scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)showed that the acclimated biogranules in the two reactors differed in microstructure.Calcium carbonate was found to have precipitated on the surface of acetate-degrading biogranules,but precipitated at the core of the carbohydrate-degrading biogranules.The results indicated that substrates had significant influence on the location of calcium carbonate precipitation in anaerobic granular sludge,which was expected due to the different methanogens distribution and pH gradient within the granular sludge degrading various substrates.Moreover,the location of calcium carbonate precipitation substantially affected the specific methanogenic activity(SMA)of the granular sludge.The SMA of the acetate-degrading biogranules dropped from 1.96 gCODCH4·gVSS^(–1)·d^(–1)to 0.61 gCODCH4·gVSS^(–1)·d^(–1)after 180-d of operation in the reactor.However,the SMA of the carbohydrate-degrading biogranules was not adversely affected by calcium carbonate precipitation.

Non-linear Viscoelastic Rheological Properties of PCC/PEG Suspensions

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ （δ is the out-of-phase angle） vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region.

Polymorph and morphology of CaCO_3 in relation to precipitation conditions in a bubbling system

Simulating the typical carbonation step in a mineral CO_2 sequestration, precipitated calcium carbonate(PCC) was prepared by bubbling CO_2 gas into a rich Ca solution. These carbonation reactions were conducted at three p H ranges, namely 10.0–9.0, 9.0–8.0, and 8.0–7.0, in which temperature and CO_2 flow rate are additional experimental variables. The PCC obtained in experiments was examined by Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD). It was found that supersaturation determined by p H value and flow rate of CO_2 has significant influence on polymorph of PCC. Vaterite was preferably formed at high supersaturation, while dissolution of metastable vaterite and crystallization of calcite occurred at low supersaturation. High temperature is a critical factor for the formation of aragonite. At 70 °C, vaterite, calcite and aragonite were observed to coexist in PCC because transformation from vaterite to aragonite via calcite occurred at this temperature. Scanning electron microscopy(SEM) technology was performed on prepared PCC, and various morphologies consistent with polymorphs were observed.

造纸专用PCC及其生产要点与应用

造纸工业是国内碳酸钙最具开发潜力的应用领域,已引起业内高度重视。该文简要介绍了造纸专用轻质碳酸钙(PCC)的国内外基本概况、质量要求、生产技术要点和实际应用案例。

Agglomeration Mechanisms and Kinetics during the Carbonation of a Suspension of Lime in a Pilot Batch Reactor

The reaction studied in this work is the synthesis of nanometric size calcium carbonate particles by carbonation of a suspension of lime, which represents the most common industrial route. It consists in bubbling carbon dioxide in a suspension of lime to obtain precipitated calcium carbonate (PCC). PCC is a mineral filler with various applications: sealants, paints, paper, ink, pharmacy, cosmetics, food etc. However, there is a challenge related to the synthesis and the use of this precipitate: the agglomeration of the monoparticles. The aim of this work is then to understand the mechanisms of this phenomenon and to study its kinetics to improve the run of the process and the control of its impact on the final product. Experiments realized with a high concentration in sodium chloride (2 M) showed that the modification of the electrostatic environment did not change the particle size distribution and the morphology of the agglomerates. This indicates that the electrostatic interactions are not responsible for the agglomeration but the formation of crystalline bridges induced by the crystal growth. Thus, thanks to an agglomeration model including the crystal growth rate, the agglomeration kernel β and the agglomeration constant β0 can be determined using a mathematical treatment of the experimental particle size distributions. Finally, by varying the experimental conditions, it appears that the agglomeration constant increases with the temperature whereas there is an optimal value regarding the shear rate.