微生物沉积碳酸钙固化砂土试验研究

砂土固化对增加砂土强度、减小渗透性极为有利,可提高和改善砂土的力学特性。通过培养基L进行菌种繁殖,研究了不同条件下的细菌生长特性;分析流出液的pH值和Ca~(2+)浓度的内在关系,揭示了固化砂柱的渗透性、无侧限抗压强度变化规律;通过微观结构阐释微生物固化效果,并研究了Ca~(2+)浓度与试样强度的关系。结果表明:2mL细菌母液加入100mL培养液并在30℃、pH为6,150rpm振动速度的条件下最适宜菌种生长;固化过程中,pH值逐渐降低,而Ca~(2+)浓度则增大;采用0.5mol/L胶凝液固化效果较好且固化周期短;固化后砂土颗粒间孔隙被生成的碳酸钙填充;试样渗透性最终降低3~4个数量级;流速越小,固化时间越长,固化效果越好;且固化试样破坏模式都是脆性破坏;采用尿素和醋酸钙混合溶液作为胶凝液,更能提高Ca~(2+)利用率。     

Performance of microbial-induced carbonate precipitation on wind erosion control of sandy soil

Wind erosion is a serious problem throughout the world which results in soil and environment degradation and air pollution. The main objective of this study was to evaluate feasibility of microbial-induced carbonate precipitation, as a novel soil-strengthening technique, to reduce wind erosion risk of a sandy soil. For this purpose, the erosion of biocemented soil samples was investigated experimentally in a wind tunnel under the condition of wind velocity of 45 km h^?1. The weight loss of treated samples relative to the weight loss of control treatment was 1.29 and 0.16 % for low and high bacterial mix concentrations, respectively, indicating a significant improvement in erosion control in biologically treated samples. The effect of biological treatment on wind erosion control was even superior at the higher velocities. Thereafter, the penetration resistance of the surface layers as a simple index of resistance against wind erosion was measured. Significant improvements in the penetration resistance of the treated soil samples were observed. Although low bacterial mix concentrations did not significantly improve the penetration resistance of the samples, significant improvements in the penetration resistance of the treated soil samples were observed reaching to the highest measured strength (56 kPa) in high bacterial mix concentrations samples. Finally, the morphology of precipitated CaCO₃ crystals using scanning electron microscopy and X-ray powder diffraction analysis showed that the CaCO₃ was mainly precipitated as vaterite crystals forming point-to-point contacts between the sand granules.     

Effect of multiple precipitation inhibitors on calcium carbonate nucleation

Understanding the factors which affect the precipitation of calcium carbonate is important to the study of most natural waters. The effect of blends of precipitation inhibitors on calcium carbonate nucleation is investigated via a new test apparatus. Results indicate that the behavior of mixed inhibitors at minimum concentration levels is strictly additive, as predicted theoretically. The potential existence of a “super effective” inhibitor in nature or in industry is therefore precluded; this may have significant consequences for water-processing industries. The possibility of extending the upper limit of inhibitor effectiveness, imposed by the solubility of the calcium-inhibitor salts, through the use of mixed inhibitors is discussed. It is also possible that the notion of additive effects of mixed inhibitors may be valid in other systems, such as geochemical environments, potable water treatment systems, and industrial waters in which naturally occurring calcium carbonate inhibitors exist.     

Bio-mediated calcium carbonate precipitation and its effect on the shear behaviour of calcareous sand

Calcareous sands have abundant intraparticle pores and are prone to particle breakage. This often leads to poor engineering properties, which poses a challenge to coastal infrastructure construction. A study using bio-cementation to improve the engineering properties of calcareous sand is presented in this paper. The macro- and microscopic properties of bio-cemented calcareous sand were characterized by drained triaxial tests and scanning electron microscopy observations. Experimental results show that the precipitated calcium carbonate can effectively fill the intra- and interparticle pores and bond adjacent particles, thus enhancing the shear strength of calcareous sand. The special structures (e.g. abundant intraparticle pores and rough surface) and mineral components (i.e. calcium carbonate) of calcareous sand are beneficial for improving bacterial retention in soil, which leads to a relatively uniform and dense calcium carbonate distribution on the sand particle surface, exhibiting a layer-by-layer growth pattern. This growth pattern and the abundant interparticle pores would result in less effective calcium carbonate. The strength enhancement of bio-cemented calcareous sand is significantly lower than that of bio-cemented silica sand at the same calcium carbonate content, which may be caused by the differences in the following: (a) soil skeleton strength; (b) the amount of effective calcium carbonate; and (c) interparticle pore-filling of calcium carbonate.

     

微生物沉积碳酸钙固化珊瑚砂的试验研究

向珊瑚砂中注入巴斯德芽孢杆菌菌液、氯化钙和尿素的混合液,利用微生物沉积碳酸钙固化珊瑚砂;并对珊瑚砂固化体进行了渗透、强度及微观结构等试验。试验结果表明,巴斯德芽孢杆菌的活性随时间呈衰减趋势,但衰减速度缓慢,能较好地满足珊瑚砂固化的需要。随着菌液、氯化钙和尿素的混合液注入次数的增加,珊瑚砂柱渗透性逐步降低,最终渗透性降低了1～2个数量级。微生物固化后的珊瑚砂柱应力-应变曲线大致可分为3段,即应力随应变缓慢增加段、快速增加段以及突降段。试样发生压裂脆性破坏,无侧限抗压强度最高达到14 MPa左右。抗压强度随干密度增加而增大,随渗透性降低而增大。微生物固化后珊瑚砂颗粒被生成的碳酸钙完整的包裹,孔隙间极少见生成的碳酸钙,与普通硅砂微生物固化后的微观结构不同,较好地解释了渗透性降低不多的原因。     

黄豆脲酶诱导碳酸钙沉淀多变量试验研究

植物源脲酶诱导碳酸钙沉淀（enzyme induced carbonate precipitation,简称EICP）可以显著改善砂土的工程力学特性,但在具体操作时,参数取值无对应规范,固化效果有待提升。基于黄豆脲酶,研究了温度、脲酶浓度、尿素浓度、钙浓度、pH值、钙源种类等变量对脲酶活性与碳酸钙沉淀的影响,并进行了沉淀物（碳酸钙晶体）的扫描式电子显微镜（scanning electron microscope,简称SEM）与X射线衍射（X-ray diffraction,简称XRD）测试,在此基础上开展了黄豆脲酶固化砂的无侧限抗压强度与固化效果试验研究。结果表明：脲酶活性随脲酶浓度的增加而线性增长,但存在温度阈值,温度超过阈值后,脲酶将完全失活,且阈值随脲酶浓度的增大而降低;尿素浓度与pH值共同影响脲酶活性,二者存在一个最优组合,当尿素浓度在0.1～1.0 mol/L时最优pH值为7,当尿素浓度在1.0～1.5 mol/L时最优pH值为8。脲酶是沉淀反应的催化剂,脲酶浓度越高,反应越完全,碳酸钙沉淀率越高;尿素与钙溶液则主要通过掺入量影响碳酸钙沉淀量,掺量比例宜为1:1,且二者浓度与pH值可通过影响脲酶活性来影响碳酸钙的沉淀情况;不同钙源对碳酸钙沉淀量的影响幅度不大。不同钙源沉淀碳酸钙晶体的成分与密度基本相同,但晶体结构差异较大,氯化钙沉淀碳酸钙晶体以块状为主,表面分布球状、类球状晶体,胶结面大,可作为EICP技术中较为理想的钙源。基于黄豆脲酶和氯化钙钙源固化砂的无侧限抗压强度约为掺粉煤灰砂样的6倍,通过SEM图像可发现,沉淀碳酸钙晶体包裹并黏结砂粒成为整体,固化效果非常理想。     

Kinetic fractionation of carbon-13 during calcium carbonate precipitation

Kinetic isotope fractionation of ¹³C during precipitation of CaCO₃ under open system conditions has been investigated. The isotope enrichment factor ?_HCO3^?-CaCO₃ varies between ?0.35 ± 0.23 and ?3.37 ± 0.36%. at 25°C depending on the rate of precipitation and mineralogy, the enrichment of ¹³C in the solid carbonate phase decreasing with increasing precipitation rate. An estimate of equilibrium ?_HCO3-Calcite of between ?1.83 ± 0.32 and ?2.26 ± 0.31%. is calculated from slow precipitation runs. A surface diffusion crystal growth model is used to describe the combination of kinetic isotope effects on thermodynamic isotope fractionation during rapid diffusion controlled crystal growth. Under slow precipitation conditions ?_{Calcite-Aragonite} was estimated as ?1.4%.; however, during rapid precipitation this fractionation appears to diminish and aragonite becomes less enriched in ¹³C.     

单生卵囊藻对DIC的利用及其对CaCO_3沉积影响的研究

以生长在钙华池中的单生卵囊藻（Oocystis solitaria Wittr）为研究对象,利用pH漂移方法,探讨了封闭系统中单生卵囊藻在岩溶水和非岩溶水环境下对溶解无机碳（DIC）利用及其对水体Ca^2＋沉积影响的差异。结果表明,单生卵囊藻在低CO2浓度时,通过胞外碳酸酐酶的催化,以HCO3^-作为无机碳源进行光合作用。在岩溶水环境下单生卵囊藻DIC利用能力要高于非岩溶水环境（4．78倍）,而在此过程中对水体中Ca^2＋沉积的影响也更高（2．13倍）。在岩溶水（非岩溶水）环境下,有42．6％（8．9％）的Ca^2＋通过物理化学效应以CaCO3形式沉积,其余Ca^2＋可能被藻体生长而吸收利用．．     

基于生物诱导碳酸钙沉淀的土体固化研究进展

基于微生物或脲酶诱导碳酸钙沉淀（MICP/EICP）的土体固化技术是近年来岩土和地质工程领域的研究热点之一。在系统回顾基于生物诱导碳酸钙沉淀的土体固化技术发展历程的基础上,重点阐述了MICP/EICP固化机制、土体孔隙结构、菌液和脲酶性质、胶凝液性质和固化方式等方面对碳酸钙特性影响的研究进展。研究结果表明：土体孔隙越小,越不利于微生物或脲酶入渗,固化均匀性越差;土颗粒接触点越多,可为碳酸钙提供的沉积点位越多,碳酸钙与土颗粒间的黏结和桥接作用越强,固化效果越好;一定菌液或脲酶浓度或脲酶活性范围内,碳酸钙的生成速率和生成总量随浓度及活性的增大而增大,但过高的浓度或活性易导致碳酸钙生成速率过快,从而在土体注入端发生堵塞;低浓度胶凝液得到的碳酸钙晶体更小,在土体中的分布更均匀;采用合适的注浆饱和度可提高具有黏结作用的碳酸钙的占比;采用多层交替注入或单相低pH值注入可提高碳酸钙在试样中分布的均匀性。基于碳酸钙沉淀特性的影响因素,提高固化土体的均匀性,验证其耐久性,室内试验结果在现场尺度的适应性和改进方案应该成为以后研究的重点。     

Improvement in silty sand with enzyme-induced carbonate precipitation: laboratory model experiment

Acta Geotechnica - Enzyme-induced carbonate precipitation (EICP) is a promising method for the improvement in soil properties. In this study, a model test using a meter-scale soil model was carried...     

Geophysical monitoring and reactive transport modeling of ureolytically-driven calcium carbonate precipitation

Ureolytically-driven calcium carbonate precipitation is the basis for a promising in-situ remediation method for sequestration of divalent radionuclide and trace metal ions. It has also been proposed for use in geotechnical engineering for soil strengthening applications. Monitoring the occurrence, spatial distribution, and temporal evolution of calcium carbonate precipitation in the subsurface is critical for evaluating the performance of this technology and for developing the predictive models needed for engineering application. In this study, we conducted laboratory column experiments using natural sediment and groundwater to evaluate the utility of geophysical (complex resistivity and seismic) sensing methods, dynamic synchrotron x-ray computed tomography (micro-CT), and reactive transport modeling for tracking ureolytically-driven calcium carbonate precipitation processes under site relevant conditions. Reactive transport modeling with TOUGHREACT successfully simulated the changes of the major chemical components during urea hydrolysis. Even at the relatively low level of urea hydrolysis observed in the experiments, the simulations predicted an enhanced calcium carbonate precipitation rate that was 3-4 times greater than the baseline level. Reactive transport modeling results, geophysical monitoring data and micro-CT imaging correlated well with reaction processes validated by geochemical data. In particular, increases in ionic strength of the pore fluid during urea hydrolysis predicted by geochemical modeling were successfully captured by electrical conductivity measurements and confirmed by geochemical data. The low level of urea hydrolysis and calcium carbonate precipitation suggested by the model and geochemical data was corroborated by minor changes in seismic P-wave velocity measurements and micro-CT imaging; the latter provided direct evidence of sparsely distributed calcium carbonate precipitation. Ion exchange processes promoted through NH4+ production during urea hydrolysis were incorporated in the model and captured critical changes in the major metal species. The electrical phase increases were potentially due to ion exchange processes that modified charge structure at mineral/water interfaces. Our study revealed the potential of geophysical monitoring for geochemical changes during urea hydrolysis and the advantages of combining multiple approaches to understand complex biogeochemical processes in the subsurface.     

Interaction between dissolved silica and calcium carbonate: 1. Spontaneous precipitation of calcium carbonate in the presence of dissolved silica

The kinetics of spontaneous precipitation of CaCO₃ from aqueous solution in the presence of dissolved silica was investigated by recording pH as a function of time. The presence of dissolved silica, at concentrations below saturation with respect to the amorphous phase, decreases induction time for CaCO₃ nucleation, but does not affect CaCO₃ polymorphism. For a “pure” system without silica, the surface free energy, σ, determined from classical nucleation theory is 42 mJ m⁻². This agrees well with values reported in the literature for vaterite and indicates some degree of heterogeneous nucleation, which can occur because of the relatively low degree of supersaturation used for the experiments. In the presence of 1 and 2 mM silica, σ is 37 and 34 mJ m⁻², indicating an increasing degree of heterogeneous nucleation as the amount of polymeric silica increases. The ratio of Ca²⁺ to CO₃²⁻ activity was a governing parameter for determining which CaCO₃ polymorph precipitated. At high Ca²⁺ to CO₃²⁻ activity ratios, almost all initial solid was vaterite, whereas at low ratios, a mixture of vaterite and calcite was observed. In solutions with low Ca²⁺ to CO₃²⁻ activity ratios, the presence of silica at concentrations above saturation with respect to amorphous silica led to formation of only calcite and strongly influenced the crystalline structure and morphology of the precipitates. At high Ca²⁺ to CO₃²⁻ ratios, system behaviour did not differ from that without silica.     

The significance of Chara vegetation in the precipitation of lacustrine calcium carbonate

A significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and, in addition, macrophytes in the littoral zone. Lake Wigry, one of the largest lakes in Poland (north‐east Poland), is characterized by: (i) carbonate sediments with a CaCO₃ content exceeding 80% within the littoral zone; and (ii) large areas of submerged vegetation dominated by charophytes (macroscopic green algae, Characeae family). It is claimed that charophytes are highly effective in utilizing HCO₃^? and forming thick CaCO₃ encrustations. Thus, this study was aimed at evaluating the CaCO₃ production by dense Chara stands overgrowing the lake bottom reaching a depth of 4 m. In late July 2009, the fresh and dry mass of plants, the percentage contribution of calcium carbonate and the production of CaCO₃ per 1 m² were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0·0625 m²) per transect. The composition and structure of phytoplankton and the physico‐chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake. The greatest dry plant mass exceeded 1000 g m^?2 and CaCO₃ encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685·5 and 438 g m^?2, respectively, which exceeded previously reported results. A correlation of carbonate production with the depth of Chara stands was detected, and intermediate depths offered the most favourable conditions for carbonate precipitation (589 g m^?2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO₃ sedimentation.     

微生物沉积碳酸钙固化砂质黏性紫色土试验研究

重庆紫色土是一种砂质黏性土,地区降雨集中,水力冲蚀作用剧烈,极易产生水土流失,微生物诱导方解石沉积(MICP)技术因能耗低、污染小而广泛应用于土体加固中。通过正交试验优化了巨大芽孢杆菌(BNCC 336739)的培养基和培养条件,活菌数增长126%,活性良好。采用巨大芽孢杆菌,进行低水压(9.8kPa)灌注固化砂质黏性紫色土试验,探究了固化效果的变化规律。结果表明:随固化次数增加,碳酸钙生成量和干密度逐级增加,无侧限抗压强度与碳酸钙生成量正相关;碳酸钙有效沉积越来越少,强度提高趋于稳定,固化9次后强度提高77%;随孔隙被碳酸钙填充和上下碳酸钙硬壳的形成,渗透性不断降低,最终下降两个数量级;通过试样上、中、下三部分碳酸钙生成量C的样本标准差s来反映碳酸钙分布离散程度,发现割线弹性模量在s的影响下随C增加而波动上升,波动表现为在C相近或s相差很大时,s越小割线弹性模量越大。研究成果可以为MICP技术在紫色土地区的地基、边坡加固和水土流失防护等工程应用提供科学依据和参考。     

Influence of lysozyme on the precipitation of calcium carbonate: a kinetic and morphologic study

Several mechanisms have been proposed to explain the interactions between proteins and mineral surfaces, among them a combination of electrostatic, stereochemical interactions and molecular recognition between the protein and the crystal surface. To identify the mechanisms of interaction in the lysozyme-calcium carbonate model system, the effect of this protein on the precipitation kinetics and morphology of calcite crystals was examined. The solution chemistry and morphology of the solid were monitored over time in a set of time-series free-drift experiments in which CaCO₃ was precipitated from solution in a closed system at 25°C and 1 atm total pressure, in the presence and absence of lysozyme. The precipitation of calcite was preceded by the precipitation of a metastable phase that later dissolved and gave rise to calcite as the sole phase. With increasing lysozyme concentration, the nucleation of both the metastable phase and calcite occurred at lower Ω_calcite, indicating that lysozyme favored the nucleation of both phases. Calcite growth rate was not affected by the presence of lysozyme, at least at protein concentrations ranging from 0 mg/mL to 10 mg/mL.Lysozyme modified the habit of calcite crystals. The degree of habit modification changed with protein concentration. At lower concentrations of lysozyme, the typical rhombohedral habit of calcite crystals was modified by the expression of {110} faces, which resulted from the preferential adsorption of protein on these faces. With increasing lysozyme concentration, the growth of {110}, {100}, and finally {001} faces was sequentially inhibited. This adsorption sequence may be explained by an electrostatic interaction between lysozyme and calcite, in which the inhibition of the growth of {110}, {100}, and {001} faces could be explained by a combined effect of the density of carbonate groups in the calcite face and the specific orientation (perpendicular) of these carbonate groups with respect to the calcite surface. Overgrowth of calcite in the presence of lysozyme demonstrated that the protein favored and controlled the nucleation on the calcite substrate. Overgrowth crystals nucleated epitaxially in lines which run diagonal to rhombohedral {104} faces.     

微生物矿化作用改善岩土材料性能的影响因素

基于微生物诱导碳酸钙沉淀作用（MICP）的土体改性技术近年来在岩土工程领域引起了人们的广泛关注。该技术在改善岩土材料的强度、刚度、抗液化、抗侵蚀及抗渗透性等性能的同时,还能维持土体良好的透气性和透水性,改善植物的生长环境。由于微生物矿化作用涉及一系列生物化学和离子化学反应,固化过程中的反应步骤较多,因此,MICP固化效果受许多因素的制约与影响。基于大量文献资料,系统总结了细菌种类、菌液浓度、温度、pH值、胶结液配比及土的性质等关键因素对微生物改善岩土材料性能的影响,讨论了这些影响因素的优化方式和未来的研究方向,主要得到了以下几点结论：菌种类型、菌液浓度、温度、pH、胶结液性质会从微观上影响碳酸钙的晶体类型、形貌和尺寸,进而在宏观层面影响岩土体的胶结效果;菌液浓度尽可能高、温度在20～40℃间、pH值在7.0～9.5左右、胶结液浓度在1 mol/L以内的因素条件对微生物加固岩土体具有较好的效果。上述范围内的低温、较高的pH值、低浓度胶结液有助于提高土体的抗渗性,而高温、较低的pH值以及中高浓度胶结液有助于提高土体的强度;MICP加固土体的有效粒径范围为10～1 000 ?m,相对密度越大、级配越好则加固效果越好。分步灌浆法、多浓度相灌注法及电渗灌浆法有助于提高土体固化均匀性,0.042 (mol/L)/h以下的注浆速度有利于提高胶结液利用率,砂土试样的灌浆压力一般在10～30 kPa之间,粉黏土试样的灌浆压力不宜超过110 kPa,过高的灌浆压力会破坏土体结构,降低固化效果。     

Insight into the mechanism of microbially induced carbonate precipitation treatment of bio-improved calcareous sand particles

Acta Geotechnica - The use of the calcareous soil as a backfill material in ocean constructions faces pervasive challenges due to the significant rate of particle fracture. To meet the requirements...     

An experimental study of mitigating coastal sand dune erosion by microbial- and enzymatic-induced carbonate precipitation

Acta Geotechnica - Due to more extreme weather events and accelerating sea-level rise, coastal sand dunes are subjected to more frequent storm wave inundation and surge impacts, which contribute to...     

酶诱导碳酸钙沉淀加固遗址土动力特性试验研究

中国西北地区地震频发,土遗址长期受到地震活动的不利影响。为了研究酶诱导碳酸钙沉淀技术（EICP）加固遗址土的动力特性,对1.55、1.65、1.75 g/cm³这3种初始干密度的遗址土进行EICP处理,并设置未经EICP处理的对照组。开展了不同围压、振动频率下的动三轴试验。结果表明：在相同动应力作用下,相比对照组,试验组的动应变更小,耗散的能量更少,阻尼比更小;在EICP加固后,随着干密度、围压、振动频率增大,可以降低动应变的产生,但这种效果依次减弱。动本构关系符合Hardin模型,干密度、围压、振动频率对模型参数a（动弹性模量）的影响程度逐渐减小;微观分析发现,EICP加固后,碳酸钙沉淀在土颗粒表面附着,填充孔隙,并与土颗粒相互胶结成致密结构,土体结构强度增强。     

Creation of an artificial carbonate sand

This paper deals with the efficacy of creating artificial carbonate sand from crushed chalk to model the natural carbonate sand. Direct drained shear using 100 mm shear box and compressibility tests using 150 mm Rowe cell have been performed on artificial carbonate sand in order to determine the shear stress-strain and compressibility characteristics of the artificial material. These are compared with data from natural carbonate sands given in the literature. The results obtained demonstrate that shear stress-strain and compressibility characteristics of the artificial material closely mirror that of natural carbonate soils. The artificial carbonate sand shows generally similar characteristics, which are in the range of the natural carbonate material.