Experimental study on CO2 capture conditions of a fluidized bed limestone decomposition reactor

In this study, the decomposition conditions of limestone particles (0.25-0.50 mm) for CO₂ capture in a steam dilution atmosphere (20-100% steam in CO₂) were investigated by using a continuously operating fluidized bed reactor. The results show that the decomposition conversion of limestone increased with the steam dilution percentage in the CO₂ supply gas. At a bed temperature of 920 °C, the conversions were 72% without steam dilution and 98% with 60% steam dilution. The conversion was 99% with 100% steam dilution at 850 °C of the bed temperature. Steam dilution can decrease not only the decomposition temperature of limestone, but also the residence time required for nearly complete decomposition of CaCO₃. The hydration and carbonation reactivities of the CaO produced were also tested and the results show that both the reactivities increased with the steam dilution percentage for decomposing limestone.     

Sulfate ingress in Portland cement

The interaction of mortar with sulfate solutions leads to a reaction front within the porous material and to expansion. Thermodynamic modelling coupled with transport codes was used to predict sulfate ingress. Alternatively, “pure” thermodynamic models - without consideration of transport - were used as a fast alternative to coupled models: they are more flexible and allow easy parameter variations but the results relate neither to distance nor to time. Both transport and pure thermodynamic modelling gave comparable results and were able to reproduce the changes observed in experiments. The calculated total volume of the solids did not exceed the initial volume of the paste indicating that not the overall volume restriction leads to the observed expansion but rather the formation of ettringite within the matrix and the development of crystallisation pressure in small pores. The calculations indicate that periodic changing of the Na₂SO₄ solution results in more intense degradation.     

Calcination and sintering characteristics of limestone under O2/CO2 combustion atmosphere

The O₂/CO₂ coal combustion technology is an innovative combustion technology that can control CO₂, SO₂ and NO_x emissions simultaneously. Calcination and sintering characteristics of limestone under O₂/CO₂ atmosphere were investigated in this paper. The pore size, the specific pore volume and the specific surface area of CaO calcined were measured by N₂ adsorption method. The grain size of CaO calcined was determined by XRD analysis. The specific pore volume and the specific surface area of CaO calcined in O₂/CO₂ atmosphere are less than that of CaO calcined in air at the same temperature. And the pore diameter of CaO calcined in O₂/CO₂ atmosphere is larger than that in air. The specific pore volume and the specific surface area of CaO calcined in O₂/CO₂ atmosphere increase initially with temperature, and then decline as temperature exceeds 1000 °C. The peaks of the specific pore volume and the specific surface area appear at 1000 °C. The specific surface area decreases with increase in the grain size of CaO calcined. The correlations of the grain size with the specific surface area and the specific pore volume can be expressed as L = 744.67 + 464.64 lg(1 / S) and L = − 608.5 + 1342.42 lg(1 / ε), respectively. Sintering has influence on the pore structure of CaO calcined by means of influencing the grain size of CaO.     

Process development for the removal of copper from wastewater using ferric/limestone treatment

The removal of copper from wastewater by ferric/limestone coagulation followed by screen filtration was carried out at a laboratory scale. The optimum coagulant (FeCl₃) dose and working pH were 50 mg// of Fe(m) and pH 7.5, respectively, through jar tests. For the efficient removal of copper from wastewater, we developed a novel process including the co-precipitation of copper with FeCl₃, alkalization in a limestone aeration bed, and separation of precipitates in a sedimentation tank coupled with internal stainless steel screen filter. The performance results showed that removal of copper from the solution was over 99.5%. The pH was effectively maintained over 7.5 in limestone bed during the whole process. Ferric hydroxide/copper aggregates were removed over 99% by stainless steel screen filter of 1,450 mesh. Periodic air backwashing alleviated fouling of the filter surface.     

管桩生产中石灰石集料对混凝土强度的影响

采用石质为石灰石与石质为硅质岩的两种不同粗集料拌制混凝土,经过常压养护、压蒸养护等不同的混凝土蒸汽养护工艺,测定混凝土脱模抗压强度及压蒸后抗压强度。结果表明:石质为石灰石与石质为花岗岩的两种不同粗集料在常压养护结束后,混凝土抗压强度均有较大的增长,混凝土强度增长规律基本一致;但经压蒸养护后石质为石灰石与石质为花岗岩的两种不同粗集料配制的混凝土抗压强度产生很大的差异,石质为石灰石的粗集料配制的混凝土强度增长较低,而石质为硅质岩的粗集料配制的混凝土强度有很大的提高。     

Effect of limestone filler on the deterioration of mortars and pastes exposed to sulfate solutions at ambient temperature

This paper presents data on engineering properties such as compressive strength, visual change and expansion of mortar specimens incorporating limestone filler subjected to severe sulfate attack at ambient temperature. Specimens with four replacement levels of limestone filler (0, 10, 20 and 30% of cement by mass) were immersed in sodium and magnesium sulfate solutions with 33,800 ppm of SO₄²⁻ concentration. In order to identify the products formed by sulfate attack, microstructural analyses such as XRD and SEM were also performed on the paste samples with similar replacement levels of limestone filler.The test results demonstrated that mortar and paste samples incorporating higher replacement levels of limestone filler were more susceptible to sulfate attack irrespective of types of attacking sources. However, the deterioration modes were significantly dependent on the types of sulfate solutions. Additionally, although the samples were exposed to sulfate solutions at 20 ± 1 °C, the deterioration was strongly associated with thaumasite formation in both sulfate solutions.The deterioration mechanism and resistance to sulfate attack of cement matrix incorporating limestone filler at ambient temperature is discussed in the light of the test results obtained.     

Relationship between Texas Cone Penetrometer Tests and Axial Resistances of Drilled Shafts Socketed in Clay Shale and Limestone

Modern methods for designing drilled shafts in soft rock require knowledge of the compressive strength and modulus of the rock. However, rock jointing at many sites prohibits the recovery of samples of sufficient length and integrity to test rock cores in either unconfined or triaxial compression tests. Since rational design procedures usually require values of compressive strength, surrogate methods must be employed to estimate the compressive strength of the rock. The surrogate methods considered in this study was Texas cone penetrometer tests, and performed at several sites in North Central Texas. In order to develop the relationships between Texas cone penetrations and side and base resistances of rock socketed drilled shafts, three field load tests were conducted. Based on the field study and literature reviews, a relationship between Texas cone penetration tests and axial resistances of rock socketed drilled shafts was proposed.     

露天矿爆破效果影响因素分析

爆破是露天矿生产的重要环节，本文根据七峰山石灰石矿多年的生产实践，从几方面简要分析了影响露天矿爆破效果的一些因素。对类似矿山的爆破实践有积极的指导意义。     

Molecular monitoring of the microbial dynamics occurring on historical limestone buildings during and after the in situ application of different bio-consolidation treatments

Microbially Induced Carbonate Precipitation is proposed as an environmentally friendly method to protect decayed ornamental stone and introduced in the field of preservation of Cultural Heritage. Recent conservation studies performed under laboratory conditions on non-sterile calcarenite stones have successfully reported on the application of a suitable nutritional solution, inoculated and non-inoculated with Myxococcus xanthus, as a bioconsolidation treatment. Furthermore, this procedure has been applied in situ, very recently, to selected historical buildings in Granada, Spain. For the first time, we evaluate the efficiency and risks of the in situ application of the above mentioned treatments onto two historical buildings in Granada. The evaluation consists of a detailed investigation of the micro-biota actively growing during the seven days of the treatments - short-term monitoring and of that remaining on the stones after six and twelve months of the application - long-term monitoring. A molecular strategy, including DNA extraction, PCR amplification of 16S rRNA sequences, construction of clone libraries and fingerprinting by DGGE (Denaturing Gradient Gel Electrophoresis) analysis followed by sequencing was used to gain insight into the microbial diversity present on the differentially treated stones. The monitoring of M. xanthus was performed by PCR using species-specific primers. Similar dynamics were triggered on both buildings by the application of the nutritional solution (inoculated or non-inoculated). 16S rDNA sequencing revealed the dominant occurrence of members belonging to the Firmicutes and Proteobacteria during the seven days of the treatment, whereas after one year the order Bacillales of the phylum Firmicutes was the predominantly detected microorganisms. M. xanthus could be detected only during the seven days of the treatment. The treatments seem to activate no dangerous microorganisms and furthermore, to select the remainder of a homogeneous group of carbonatogenic bacteria on the stones after a long period of time.     

清水茶咀窑石灰石矿采空区稳定性分析与治理

为研究清水茶咀窑石灰石矿采空区稳定性,在对采空区及其开采环境进行现场调研的基础上,进行了现场点荷载试验与室内单轴抗拉、抗压强度试验,获得了岩体力学参数。采用三维有限元方法对清水茶咀窑石灰石矿进行数值模拟,模拟结果表明：清水茶咀窑石灰石矿不稳定,空区顶板拉应力集中,有可能出现顶板冒落或片帮,并且地表沉陷比较大。根据分析结果与现场调查情况,提出了相应安全对策,为矿山的安全生产有指导作用。