Dissolution Precipitation Wave Structure of Hydrothermal Ore Zoning

Hydrothermal ore zoning is a transport-reaction problem in which infiltration is the principal Prcness of transport and dissolution/Precipitation is the Principal process of chemical reactions.Neglecting diffusion and ion exchange/adsorption would not affect the basic attributes of hydrothermal ore zoning. Hydrothermal ore zoning belongs essentially to infiltration metasomatic zoning, it results from the formation and propagation of dissolution/precipitation waves through Permeable media. The authors apply the theory of coupled infiltration and dissolution/precipitation reactions in Physicochemical hydrodynamics to studying the structural characteristics of dissolution/precipitation waves, and apply furthermore the coherence principle in dynamic theory of multicomponent coupled systems to revealing the dynamic mechanisms of their formation. The results of investigation verify and develop . C. 's theory of infiltration metasomatic zoning,on the one hand, raising it from the qualitative, equilibrium thermodynamic basis to the quantitative dynamic level;on the other hand, and more importantly, applying theories of Physicochemical hydrodynamics and dynamics of multicomponent coupled systems to bringing to light the dynamic mechanisms of formation of the structure of hydrothermal ore zoning, and advancing a theory of hydrothermal ore zoning, putting forward new ideas on the nature of the problem of hydrothermal ore zoning, the essence of hydrothermal ore zoning and the structural characteristics and mechanisms of formation of hydrothermal ore zoning.

Groundwater fluoride contamination:A reappraisal

Dissolution of fluorite （CaF2） and/or fluorapatite （FAP） [Cas（PO4）3F], pulled by calcite precipitation, is thought to be the dominant mechanism responsible for groundwater fluoride （F） contamination. Here, one dimensional reactive-transport models are developed to test this mechanism using the published dissolution and precipitation rate kinetics for the mineral pair FAP and calcite. Simulation results correctly show positive correlation between the aqueous concentrations of F and CO2 and negative correlation between F- and Ca^2＋. Results also show that precipitation of calcite, contrary to the present understanding, slows down the FAP dissolution by 10G orders of magnitude compared to the FAP dissolution by hydrolysis. For appreciable amount of fluoride contamination rock-water interaction time must be long and of order 106 years.

FEM analyses for influences of stress-chemical solution on THM coupling in dual-porosity rock mass

The models of stress corrosion, pressure solution and flee-face dissolution/precipitation were introduced. Taking a hypothetical nuclear waste repository in an unsaturated dual-porosity rock mass as the calculation objective, four cases were designed 1） the fracture aperture is a function of stress corrosion, pressure solution and free-face dissolution/precipitation; 2） the fracture aperture changes with stress corrosion and pressure solution; 3） the fracture aperture changes with pressure solution and free-face dissolution/precipitation; 4） the fracture aperture is only a function of pressure solution, and the matrix porosity is also a function of stress in these four cases. Then, the corresponding two-dimensional FEM analyses for the coupled thermo-hydro-mechanical processes were carried out. The results show that the effects of stress corrosion are more prominent than those of pressure solution and free-face dissolution/precipitation, and the fracture aperture and relevant permeability caused by the stress corrosion arc only about 1/5 and 1/1000 of the corresponding values created by the pressure solution and free-face dissolution/precipitation, respectively Under the action of temperature field from released heat, the negative pore and fracture pressures in the computation domain rise continuously, and are inversely proportional to the sealing of fracture aperture. The vector fields of flow velocity of fracture water in the cases with and without considering stress corrosion are obviously different. The differences between the magnitudes and distributions of stresses within the rock mass are very small in all cases.

An optimized numerical method to pre-researching the performance of solid-phase oxygen control in a non-isothermal lead–bismuth eutectic loop

In the present work,a new transient calculation method for parameters that can be used to evaluate the ability of oxygen control in a non-isothermal lead-bismuth eutectic(LBE)loop with solid-phase oxygen control was proposed.It incorporates the dissolution process of PbO particles and the oxygen mass transfer process,and an optimized method was used for finding out the optimized oxygen mass transfer coefficient.In numerical terms,three mass transfer models were simultaneously applied,and comparisons of calculated and experimental results from the CRAFT loop indicated that the optimized calculation method and these new oxygen mass transfer models were correct and applicable to other LBE loops.Through this calculation method,we aimed to optimize prediction of the distribution of oxygen and iron concentrations,time taken to establish the steady state of oxygen,and maximum dissolution/precipitation rates of corrosion products and corrosion depth across the entire LBE loop.We hope that this work will provide a potential reference for designing a more intelligent oxygen control system in the future.

Improving the Estimation of Salt Distribution during Evaporation in Saline Soil by HP1 Model

Restricted by the development of the transient flow and solute reactive transport models for unsaturated soil, empirical functions have been used previously to calculate the mass of dissolved or precipitated salt when they have to be taken into account. Besides, the solute reactive transport process has often been inferred based on measurements that cost lots of time and manpower. HP1 model coupled with PHREEQC provides a suitable tool to improve the estimation of salt distribution during evaporation in saline soil, where the salt dissolution and precipitation cannot be ignored. In this study, we compare the performance of a standard solute transport(SST) model and the HP1 model to examine the improvement of salt distribution estimation. Model results are compared with experimental data sets from four field lysimeters. These columns were exposed to Na Cl solution with different concentrations(3, 30, 100, and 250 g/L) and were undergoing the same strong evaporation boundary condition. The pre-existing Ca SO_(4), Na Cl and Na2SO_(4)loads were 1.15, 0.47 and 0.23 g/(100 g of soil), respectively. Simulation results show that HP1 ameliorates the overestimation of salt content by SST in deeper soil due to the absence of dissolution of pre-existing soluble salts, and prevents the concentration of the solute from exceeding the solubilities which would occur in SST-result. Additionally, HP1-predicted results can help trace the transport process of each solute. Based on the results, we strongly suggest that the management of fields sensitive to salt content should make use of a coupled flow and chemical reaction model.

Hydrogeochemical Modeling of the Shallow Thermal Water Evolution in Yangbajing Geothermal Field, Tibet

The exploitation of thermal water and the mix of cold water changed the properties of geofluid in shallow reservoir,which altered the concentration of the chemical constitutes and continuously built new water-rock reaction. This paper deduced reservoir pressure and temperature variation tendency from 2004 to 2013,analyzed the change of some components in the shallow reservoir water,and finally obtained the evolution of the shallow geothermal water with hydrogeochemical model. The results show the reservoir pressure decreased significantly compared with the slight decline of reservoir temperature,and much cold groundwater infiltrated into the shallow reservoir,which affected the solubility of SiO2 and led to precipitation,the increased CO2 in shallow reservoir promoted the dissolution of aluminosilicate. Calcite and kaolinite precipitation zone has extended to the north in the field,which influenced the porosity of the reservoir rock.

Synthesis of b-type Strontium Hydrogen Phosphate Nanosheets and Its Immobilization of Pb^(2+) in Acidic Aqueous Solution

Highly crystalline β-type strontium hydrogen phosphate （β-SrHPO4） nanosheets were prepared by a hydro- thermal method and used for the immobilization of lead ions （Pb2＋） from acidic aqueous solution. The effects of various parameters on the immobilization process, including solution pH value, contact time, initial ion concentrations, and coexistent competing cations, were studied to optimize the conditions for maximum immobilization. The β-SrHPO4 nanosheets exhibited a capacity of （1,120 ± 22） mg/g toward Pb2＋ in acidic solution （pH value is 3.0）, and the equilibrium was achieved within 8 rain. The competing cations such as Cu2＋, Zn2＋, Cd2＋, and Co2＋ affected slightly on the selective immobilization of Pb2＋. The results revealed that the removal mechanism of Pb2＋ by the β-SrHPO4 nanosheets was the dissolution/precipitation process in the acidic solution.