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.

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.

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.

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.

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。

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.

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.

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.

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.

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。

不同钙源EICP溶液改良路基黄土动力特性研究

由于黄土地区路基基床强度低,在长期动态压力下黄土会发生不均匀沉降、滑坡或坍塌等工程问题。为了使动荷载作用下的黄土强度更符合实际工程需要,有必要进一步研究不同钙源EICP溶液对黄土动强度的改良效果。本工作以陕西某基坑黄土为研究对象,在胶凝液中引入环保型木钙代替传统钙源进行技术改进,结合室内动三轴试验在不同围压下比较三种钙源EICP溶液对黄土的固化效果。结果表明:EICP溶液能显著提高黄土的动强度;同一围压下,黄土试样动应力和阻尼比随应变的增大逐渐升高,而动剪切模量随应变的增大逐渐降低;围压较小时,乙酸钙源EICP溶液对黄土动强度的改良效果较好,而当围压较大时,木钙源EICP溶液对黄土动强度的改良效果较好;同一试样所受围压越大,动强度和动剪切模量越大,阻尼比越小。

EICP改良膨胀土的物理力学性质试验研究

为了探究脲酶诱导碳酸钙沉淀(EICP)技术改良弱膨胀土的物理力学特性,利用大豆脲酶开展EICP技术处理弱膨胀土的膨胀特性和力学特性试验研究。通过EICP多因素配比正交试验研究脲酶浓度、初始Ca^(2+)浓度、酶胶比、尿钙比、养护时间对膨胀土碳酸钙生成率、自由膨胀率的影响及其变化规律,确定了EICP反应液最佳配比。采用不同掺量EICP反应液改良膨胀土,通过无荷载膨胀率试验、无侧限抗压强度试验及三轴压缩试验验证改良效果。结果表明:EICP反应液掺量为20%时抑制膨胀土膨胀性效果最好,且此时土体力学强度和碳酸钙生成率最高。大豆脲酶诱导产生的沉淀物为方解石型碳酸钙,附着在土颗粒表面既填充了土颗粒孔隙,也胶结了土体骨架颗粒,阻碍土体与水分接触,提高了土体密实性和黏结强度,改善了膨胀土膨胀性和力学性能。

接触溶蚀条件下混凝土游离钙离子固化效果研究

为研究将硅灰和硅酸钠作为掺合料内掺后的喷射混凝土在接触溶蚀条件下析出钙离子的规律,在不同掺量下制备了单掺和复掺混凝土试块,开展30 d去离子水浸泡试验,测试溶液中的钙离子浓度、溶液pH值的变化情况,并结合SEM等微观检测对接触溶蚀过程进行研究。结果显示:单掺硅灰试块在不换水条件下的钙离子溶出量大大低于空白组,换水条件下30 d内3%、5%、7%掺量组较空白组平均溶出钙离子总重依次减少73.29%、69.65%、69.26%;单掺硅酸钠后,不换水条件下3%掺量的试块钙离子溶出量也能得到明显的降低,换水条件下30 d内1%、3%、5%掺量组较空白组平均溶出钙离子总重依次减少9.22%、20.53%、29.96%;将单掺组中固化效果良好的3%掺量硅灰和5%掺量硅酸钠复掺入混凝土后,不换水条件下浸泡溶液初始钙离子浓度仅为20~30 mg/L,从第18天左右溶液游离钙离子清零,换水条件下复掺试块较空白组平均溶出钙离子总重减少约85%。

微生物诱导碳酸钙沉淀技术的工程应用进展与评述

基于微生物诱导碳酸钙沉淀(Microbially Induced Calcium carbonate Precipitation,MICP)技术的土体胶结固化技术是21世纪以来岩土工程、地质工程领域研究的热点之一。本文系统阐述了MICP技术的加固机理,从MICP加固效果和应用实践的角度出发,对MICP技术工程应用的研究现状进行评述。结果表明:MICP固化后的场地强度呈现出不均匀性明显、碳酸钙含量分布随深度递减的趋势;沙漠环境中,原位提取的菌种诱导生成的碳酸钙覆膜较传统的巴氏芽孢杆菌,具有更好的强度表现和稳定性;新型MICP技术应用(如微生物水泥、微生物砖)在强度、耐久性上表现出良好的应用前景,有望为实现我国双碳目标注入新的活力。基于MICP技术碳酸钙沉淀特质的影响因素,现场尺度下如何提高碳酸钙分布的均匀性以及在季节性变化下的碳酸钙骨架的耐久性、不同环境下的固化效率改进方案应该成为日后研究的重中之重。

微生物岩土工程技术的过去、现在与未来

微生物岩土工程技术作为一种新兴的生态友好型岩土体改良加固技术,应用前景广阔。但限于理论水平和研究手段,该技术仍存在较多不足,难以实现高效固化,由此成为大规模现场应用的瓶颈。而提升固化效率的关键在于明确其作用原理和影响机制。文章梳理了微生物诱导碳酸钙沉积技术(MICP)的研究现状,系统归纳了固化原理和改良岩土体的物理力学特性,并分析得出固化效率主要受到反应物自身和外部环境两方面的影响。当前MICP技术已初步应用于土体固化、裂缝修复、防渗处理、污染修复及微生物水泥等领域,但由于矿化难以均匀、反应物不经济、微生物及脲酶活性期短且受环境干扰大、代谢产物附带毒性、现场应用性差,该技术目前主要限于实验室水平。作者分别提出了可能的突破与改进方向,并结合实验室成果指出豆粕进行菌体扩培和脲酶供给的碳源优势,以及将磷石膏作为现场钙源的环保性和经济性,以期为从事微生物岩土工程研究与技术开发的人员提供参考。