西安地区二灰石试验分析

二灰石具有很多方面的优点,故在高等级公路的基层和底层得到广泛应用。本文主要针对西安地区所产二灰石,通过对其材料性能的试验以及数据的分析,所得结果对今后此地所产二灰石的质量控制有很好的支撑作用。

二灰石屑的路用性能试验研究

通过对二灰石屑进行配比、干缩、冲刷等试验,对其路用性能进行研究。通过配比试验所得数据,进行强度分析,讨论石灰与粉煤灰配合比的不同以及龄期对二灰石屑强度的影响;通过干缩试验,分析了不同配比二灰石屑的干缩性能。研究结果表明,密实型二灰石屑的干缩性能明显优于悬浮型二灰石屑;通过冲刷试验,得出二灰石屑具有较好的抗水毁能力,以上研究结论可为其作为路面基层材料提供依据。

机械摊铺二灰石施工作业控制措施

随着城镇各级道路建设的发展，道路施工的机械化程度迅速提高。施工质量与速度也都有了硬件保障。为适应这种发展，城镇道路路基的施工——机械摊铺二灰石应运而生，本文着重阐述了机械摊铺二灰石过程中的施工要点，供同类工程借鉴。

简述市政道路机铺二灰碎石基层施工工艺

西安市政道路工程把二灰碎石混合料用作道路基层是在19世纪90年代以后,施工工艺一直采用拌和厂拌合,运至现场推土机粗平后平地机精平的方式施工,该施工方法易造成粗细料离析影响二灰石基层的整体强度,材料的浪费也很严重。19世纪末高速公路发展迅猛,对工艺要求逐渐提高,机械摊铺二灰碎石基层的施工工艺在高速公路建设中已广泛应用,形成较为完备的施工控制体系。航天城管委会在道路建设中为了保证工程质量和耐久性,要求施工单位对二灰碎石施工必须采用摊铺机摊铺,在航创路、神州大道、航开路等工程建设中严格落实管委会的精神,全部采用机铺二灰碎石工艺,提高了道路路基施工质量,取得比较理想的效果。

污酸废水处理工艺及试验研究

为进一步提升矿山冶炼过程中对排污废水的处理效果,降低其处理成本,重点对含砷污酸废水和酸性含砷废水的产生来源进行综合分析,并在传统废水处理工艺流程分析的基础上提出了二段处理工艺流程,并采用戈尔膜过滤技术对出水进行处理。实践表明,所设计的污酸废水处理工艺流程不仅可保证出水满足相关标准要求,而且可达到降本增效的目的。

Synthesis of Crystalline Hydroxyapatite from CaCO_3 and CaHPO_4·2H_2O by Mechanochemical Method

The mixture of CaHPO 4·2H 2O and CaCO 3 was ground in an aqueous system under appropriate conditions to investigate the mechanochemical reaction for the synthesis of crystalline hydroxyapatite (HA) powder. Hydroxyapatite of high crystallinity powder including trace Ca 10 (PO 4) 6CO 3(OH) and Ca 9HPO 4(PO 4) 6OH can be synthesized by mechanical activation without further thermal treatment at a high temperature. The synthesis reaction during the grinding process was almost completed within 1h. The as-ground powder exhibits a particle distribution of 20-100nm in size with a spherical or rodlike morphology. The composition and degree of crystallinity of the mechanochemical synthesized hydroxyapatite powders were coincident with the cement-type hydroxyapatite.

Thermogravimetric Study and Modeling of Direct Sulfation of Limestone by Sulfur Dioxide

The direct sulfation of limestone from different sources in Iran was studiedin a thermogravimetric analyzer under atmospheric pressure. All limestone samples tested have higherthan 97% CaCO_3. Experimental conditions were as follows: particle size levels ranging from 1.6 μmto 7.8 μm, four level reaction temperatures (700℃, 750℃, 800℃ and 850℃), and two SO_2concentrations (2.4 x 10^(-3) and 3.2 x 10^(-3) mol · mol^(-1)). The particle size and temperatureshowed dominant influences on the rate and level of conversion while the effect of SO_2concentration was weak. The shrinking core model can be used to describe the behavior of thesulfation process. The reaction kinetics and diffusion mechanism are both important in controllingthe rate of the process. The two key parameters of the model, chemical rate constant K_s andeffective diffusion coefficient D_(eff) were obtained. Model predictions are in good agreement withthe experimental data.

CFD simulation with enhancement factor of sulfur dioxide absorption in the spray scrubber

A model describing the absorption process of SO2 into limestone slurry with a spray scrubber is presented. Both the physical performance of the spray liquid in the scrubber and the involved chemical reactions are analyzed in the model. A con- tinuous concentration change of H+ was solved by iterative coupling using Matlab, and it was found that there was a remarkable influence on the concentration of the other elements in the process of SO2 absorption. The calculations show that the enhancement factor exponentially grows with an increasing value of pH and logarithmically decays with an increasing value of the driving force. To verify the accuracy of the model, experiments were also carried out, and the results suggest that the model, after combining the physical performance of the spray and the enhancement factor, can more precisely describe SO2 absorption in a spray scrubber. Furthermore, a commercial computational fluid dynamics (CFD) tool is used to perform several simulations which describe and clarify the effects of variables on SO2 absorption. The results of numerical simulation can provide a basis for further design and optimization of the scrubber.

Effect of Composts,Lime and Diammonium Phosphate on the Phytoavailability of Heavy Metals in a Copper Mine Tailing Soil

Soil samples from a historic copper mine tailing site at the Parys Mountain,North Wales(UK) were amended with green waste compost(GC),GC+30% sewage sludge(GCS),lime and diammonium phosphate(DAP),to determine the effect of amendments on DTPA-and Ca(NO3)2-extractable metals in the mine tailing and on the phytoavailability of heavy metals by a lettuce(Lactuca sativa L.).Both compost were added at the rate of 10% by weight,lime was added as calcium carbonate equivalent(pH = 7) and DAP at a 2300 mg kg-1 soil level.The experiment was arranged in randomised complete design with three replicates in pots under control environment.Addition of lime resulted in the largest reduction in metal extractability with DTPA and Ca(NO3)2 and phytoavailability of Cu,Fe and Zn while DAP was effective in lowering Pb extractability and phytoavailability.With exception of Zn,all other metals extracted decreased with time after amendment applications.The distribution of heavy metals between and within the four procedures of potentially bioavailable sequential extraction(PBASE) varied significantly(P < 0.001).Stronger relationships were noted between the metals extracted with PBASE SE1 and Cu,Pb(P < 0.01) and Fe(P < 0.001) in the lettuce.These results indicate that addition of lime is sufficient to restore the vegetative cover to a high metal mine waste while DAP is good for stabilizing Pb,but its detrimental role on plant growth and the risk associated with presence of N in DAP(through N leaching) may restrict its chances for remediation of contaminated sites.

Silica-alumina molar ratio and some factors effect on the synthesis of zeolites from fly ash

In order to improve the activity and eliminate some impurities, pretreatment was used before hydrothermal synthesis. The fly ash was mixed with an aqueous NaOH solution, the alkali melted fly ash was also adopted, which is hydrothermally treated at about 104 ℃, and the liquid/solid ratio was controlled at 6：1. In order to control Si/Al molar ratio, SiO2 or Al2O3 powers were added to the fly ash. The results of XRD and SEM show that the alkali melted can activate fly ash and eliminate its quartz and mullite, along with the improvement of Si/Al molar ratio and alkalinity. In addition, zeolite Na-A changes into sodalite gradually, and nepheline is the synthesized intermediate product. Those results were discussed on the basis of a formation mechanism of zeolite from fly ash.

Beneficiation of a low grade limestone sample

Pilot scale column flotation studies were conducted on a low grade siliceous limestone ore. Silica content was reduced to less than 13g in the concentrate so that it became satisfactory for use in the paper or rubber industries. The limestone sample was crystalline and constituted primarily of calcite that contained quartz, feldspar, pyroxene, and biotite as gangue minerals. Quartz is the major silicate gangue whereas feldspar, pyroxene, and biotite exist in minor to trace quantities. Traces of pyrite were also observed within the sample. A reverse flotation process was adopted where the silicate gangue minerals were floated using two different commercial cationic collectors： Chem-750 F or Floatamine-D. The studies clearly suggest it is possible to produce a limestone concentrate assaying around 96-97% CaCO3 containing less than 1 % Si02. The effect of feed flow rate, percent solids, froth depth, and wash water on the grade and recovery of the CaC03 concentrate is discussed.

Effects of Nano Silica, Micro Silica, Fly Ash and Bottom Ash on Compressive Strength of Concrete

In this study, SCM （supplementary cementitious materials）, such as nano silica, micro silica, fly ash and bottom ash, have been evaluated for optimal level of replacement as blending material in cement and concrete. The physical and chemical properties of the above materials were first analyzed. This study focused on compressive strength of concrete with different mixes at different ages. In many cases, products made with fly ash, micro silica, nano silica and bottom ash perform better than products made without them. Test results obtained in this study indicate that up to 5% nano silica, 10% micro silica, 20-30% fly ash and 10% bottom ash could be advantageously blended with cement without adversely affecting the strength. However, optimum levels of these materials are 1-3% nano silica, 3-8% micro silica, 10% fly ash and 5% of bottom ash when we consider the strength of concrete. All percentages are defined by weight unless otherwise mentioned.

Geochemistry of the Middle to Late Permian limestones from the marginal zone of an isolated platform(Laibin,South China)

Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform （Laibin, South China）. Shale-normalized REE＋Y patterns of all samples show notably negative Ce anomalies （0.21-0.66, average 0.33）, slightly positive Gd anomalies （1.08-1.30, average 1.20）, and positive Y anomalies with superchondritic Y/Ho ratios （36-91, average 55）, which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher NdsN/YbsN ratios （0.58-1.80） than those of modern shallow seawater （0.21-0.50） suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE＋Y elements （ZREE, NdsN/YbsN, Ce/Ce＊, Gd/Gd＊, Eu/Eu＊ and Y/Ho） in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE＋Y elements： ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO3 and SiO2 contents in limestones and bedded cherts. These results imply that precipitation of CaCO3 was inhibited by that of SiO2 which was derived mainly from hydrothermal fluid, es- pecially in bedded cherts from the Tieqiao section.

Effect of Additional Carbonates on CO_2 Emission from Calcareous Soil During the Closed-Jar Incubation

The closed-jar incubation method is widely used to estimate the mineralization of soil organic C. There are two C pools （i.e., organic and inorganic C） in calcareous soil. To evaluate the effect of additional carbonates on CO2 emission from calcareous soil during closed-jar incubation, three incubation experiments were conducted by adding different types （CaCO3 and MgCO3） and amounts of carbonate to the soil. The addition of carbonates significantly increased CO2 emission from the soil; the increase ranged from 12.0~ in the CaCO3 amended soil to 460~0 in the MgCO3 amended soil during a 100-d incubation. Cumulative CO2 production at the end of the incubation was three times greater in the MgCO3 amended soil compared to the CaCO3 amended one. The CO2 emission increased with the amount of CaCO3 added to the soil. In contrast, CO2 emission decreased as the amount of MgCO3 added to the soil increased. Our results confirmed that the closed-jar incubation method could lead to an overestimate of organic C mineralization in calcareous soils. Because of its effect on soil pH and the dissolution of carbonates, HgC12 should not be used to sterili~.e calcareous soil if the experiment includes the measurement of soil CO2 production.