Efficient stabilization of dredged sludge with high water content using an improved bio-carbonation of reactive magnesia cement method

This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.

Molecular simulation study on K^＋-Cl^- ion pair in geological fluids

This paper reports a classical molecular dynamics study of the potential of mean forces(PMFs),association constants,microstructures K^+-Cl^- ion pair in supercritical fluids.The constrained MD method is used to derive the PMFs of K^+-Cl^- ion pair from 673 to 1273 K in low-density water(0.10-0.60 g/cm).The PMF results show that the contact ion-pair(CIP) state is the one most energetically favored for a K^+-Cl^- ion pair.The association constants of the K^+-Cl^- ion pair are calculated from the PMFs,indicating that the K^+-Cl^- ion pair is thermodynamically stable.It gets more stable as T increases or water density decreases.The microstructures of the K^+-Cl^- ion pair in the CIP and solvent-shared ion-pair states are characterized in detail.Moreover,we explore the structures and stabilities of the KCl-Au(I)/Cu(I) complexes by using quantum mechanical calculations.The results reveal that these complexes can remain stable for T up to1273 K,which indicates that KCl may act as a ligand complexing ore-forming metals in hydrothermal fluids.

A molecular simulation study of Cs-Cl and Cs-F ion pairs in hydrothermal fluids

Magmatic-hydrothermal processes play an important role in the transport, enrichment, and mineralization of cesium. In this study, classical molecular dynamics simulations were performed to investigate the properties of Cs-Cl and Cs-F ion pairs in hydrothermal fluids. The association constants(log_(10)K_(A)(m)) under a wide range of temperature(i.e. 298–1273 K) and fluid density(i.e. 0.1–1.0 g/cm^(3)) were derived from the potential of mean force(PMF) curves. The results indicate that CsCl and Cs-F ion pairs have similar stabilities. This is different from other alkali metal cations(e.g., Li^(+), Na^(+), and K^(+)), which prefer binding with F over Cl. The stabilities of Cs-Cl and Cs-F ion pairs increase with increasing temperature(except for the fluid density ≤ 0.1 g/cm^(3)) or decreasing fluid density, which is similar to other alkali halide ion pairs. Comparisons among the stabilities of CsCl/F and other alkali halide ion pairs indicate that the Li–F ion pair has the highest stability in hydrothermal fluids.

A molecular dynamics study of uranyl-carbonate complexes adsorbed on basal surfaces of clay minerals

We use molecular dynamics simulation to study the mechanisms involved in the adsorption of aqueous uranyl species(UO_2^(2+)) to the basal surfaces of clay minerals,including kaolinite,pyrophyllite and montmorillonite.Uranyl ion can form various complexes with carbonates,namely,[UO_2(H_2O)_5]^(2+),[UO_2(H_2O)3(CO_3)],[UO_2(H_2O)2(CO_3)_2]^(2-),[UO_2(CO_3)_3]^(4-).The simulations show that at aqueous clay interfaces,both uranyl species and surface type control the adsorption pattern.The noncarbonato and monocarbonato uranyl species can form outer-sphere complexes on siloxane surfaces through electrostatic interaction,but the dicarbonato and tricarbonato uranyl complexes rarely adsorb on the siloxane surfaces.Strong outer-sphere adsorptions of the uranylcarbonate complexes on gibbsite surfaces are observed,which are fixed by hydrogen bonds between the ligands(carbonate and/or H_2O) and surface hydroxyls.The sorption behaviors derived in this study provide new insights into understanding the migration and enrichment of uranium and other radionuclides.

河南卢氏和江西宜春两处锂矿山地表微生物群落分布特征差异及成因分析

【目的】揭示地表锂矿石表面和风化产物中细菌群落多样性特征。【方法】针对细菌16S rRNA片段扩增进行高通量测序,分析不同锂矿石表面及其风化产物中细菌群落组成、多样性及功能属性等信息。【结果】河南卢氏南阳山伟晶岩型锂矿石和江西宜春花岗岩型锂矿石表面及其风化产物的细菌群落多样性有差异。南阳山伟晶岩矿石与其风化产物、宜春花岗岩矿石表面和风化产物(NK-1、NK-1F、YK-1、YK-1F、YK-2、YK-2F、YK-3)的OTUs分别是1010、540、835、828、1117、974和604,其差异与不同的矿物组成显著关联。两矿山均有其优势微生物,在门水平上,两矿山均以放线菌门(Actinobacteria)、变形菌门(Proteobacteria)为优势菌门。同时两矿区微生物群落组成具有显著差异性(P<0.05),不同地理位置风化产物样本之间差异尤为显著(P<0.001);在属水平上,NK-1中相对丰度大于5%的属为鞘氨醇单胞菌属(Sphingomonas)、马赛菌属(Massilia);NK-1F为类芽孢杆菌属(Paenibacillus)、杆状细菌属(Bacillus)、马赛菌属(Massilia);YK-1F为芽球菌属(Blastococcus)、念珠菌固体杆菌属(Candidatus-Solibacter)、Noviherbaspirillum属、伯克霍尔德氏菌属(Burkholderia-Caballeronia-Paraburkholderia),YK-2为unidentified-Chloroplast属,YK-2F为北里孢菌属(Kitasatospora),YK-3为1174-901-12属、甲基杆菌属(Methylobacterium)。不同地理位置的矿石及其风化物样本的功能注释均涉及代谢、遗传信息处理、环境信息处理等6个代谢通路。【结论】16S rRNA高通量测序揭示不同地区锂矿石及其风化产物的细菌多样性存在差异,各具优势类群,样本间菌落组成、多样性及功能属性的差异与锂矿石化学组成、风化程度和地理分布密切相关。这项研究揭示了优势微生物类群的元素地球化学功能与含锂矿物地表风化的潜在联系,可为微生物生态分布研究及相关微生物资源开发提供新数据。