Microstructural and thermal properties of coal measure sandstone subjected to high temperatures

To study the microscopic structure,thermal and mechanical properties of sandstones under the influence of temperature,coal measure sandstones from Southwest China are adopted as the research object to carry out high-temperature tests at 25℃-1000℃.The microscopic images of sandstone after thermal treatment are obtained by means of polarizing microscopy and scanning electron microscopy(SEM).Based on thermogravimetric(TG)analysis and differential scanning calorimetric(DSC)analysis,the model function of coal measure sandstone is explored through thermal analysis kinetics(TAK)theory,and the kinetic parameters of thermal decomposition and the thermal decomposition reaction rate of rock are studied.Through the uniaxial compression experiments,the stress‒strain curves and strength characteristics of sandstone under the influence of temperature are obtained.The results show that the temperature has a significant effect on the microstructure,mineral composition and mechanical properties of sandstone.In particular,when the temperature exceeds 400℃,the thermal fracture phenomenon of rock is obvious,the activity of activated molecules is significantly enhanced,and the kinetic phenomenon of the thermal decomposition reaction of rock appears rapidly.The mechanical properties of rock are weakened under the influence of rock thermal fracture and mineral thermal decomposition.These research results can provide a reference for the analysis of surrounding rock stability and the control of disasters caused by thermal damage in areas such as underground coal gasification(UCG)channels and rock masses subjected to mine fires.

Bioleaching of soluble phosphorus from rock phosphate containing pyrite with DES-induced Acidithiobacillus ferrooxidans

The effects of Acidithiobacillus ferrooxidans(At. f) mutated with diethyl sulfate(DES) as a mutagen on the bioleaching of soluble phosphorus(P) from rock phosphate(RP) were investigated. The results show that the oxidative activity of At. f is greatly improved by 1.0%(volume fraction) of DES. Correspondingly,the highest leaching rate of soluble P is also obtained to be 14.9% by the At. f mutated,which is 85.8% higher than that of the adapted At. f without mutation. In addition,the SEM images are significantly performed that the corrosion of RP residue surfaces leached by 1.0% DES-induced At.f is much worse than that of leached by the adapted At. f. All the above indicate that the leaching efficiency of soluble P from RP with pyrite can be greatly improved by using DES-induced At. f to a certain extent.

Current re-vegetation patterns and restoration issues in degraded geological phosphorus-rich mountain areas:A synthetic analysis of Central Yunnan, SW China

China has the largest area of inland geological phosphorus-rich(GPR) mountains in the world, where vegetation restoration is key to safeguarding the environment. We reviewed the published literature and collected new data in order to analyze re-vegetation patterns and the status of plant communities in central Yunnan. The aim of our analysis was to suggest future improvements to restoration strategies in GPR mountain regions. Our results showed that spontaneous recovery was the most widespread type of restoration. N-fixing species such as Coriaria nepalensis and Alnus nepalensis play a vital role in succession. In the past, monoculture tree plantation was the primary method used in afforestation activities in central Yunnan; in recent years however, several different methods of restoration have been introduced including the use of agroforestry systems. For practical restoration, we found that spontaneous recovery was capable of delivering the best results, but that during its early stages, restoration results were affected by several factors including erosion risk, the origin of propagates and environmental variation. In contrast, methods employing human-made communities performed better in their early stages, but were constrained by higher costs and vulnerability to degradation and erosion. The use of N-fixing species such as A. nepalensis and Acacia mearnsii in plantations were unsuccessful in restoring full ecosystem functions. The success of restoration activities in GPR mountain regions could be improved through the following measures:(1) developing a better understanding of the respective advantages and disadvantages of current natural and human-engineered restoration approaches;(2) elucidating the feedback mechanism between phosphorus-rich soil and species selected for restoration, especially N-fixing species;(3) introducing market incentives aimed at encouraging specific restoration activities such as agroforestry, and improving the industry value chain.

Characterization of tricalcium phosphate solubilization by Stenotrophomonas maltophilia YC isolated from phosphate mines

The phosphate solubilizing characteristics of a strain YC, which was isolated from phosphate mines (Hubei, China), were studied in National Botanical Research Institute’s phosphate (NBRIP) growth medium containing tricalcium phosphate (TCP) as sole phosphorus (P) source. The strain YC is identified as Stenotrophomonas maltophilia (S. maltophilia) based upon the results of morphologic, physiological and biochemical characteristics and 16S rRNA sequences analysis. The results show that the strain S. maltophilia YC can solubilize TCP and release soluble P in NBRIP growth medium. A positive correlation between concentration of soluble P and population of the isolate and a negative correlation between concentration of soluble P and pH in the culture medium are observed from statistical analysis results. Moreover, gluconic acid is detected in the culture medium by HPLC analysis. It indicates that the isolate can release gluconic acid during the solubilizing experiment, which causes acidification of the culture medium and then TCP solubilization. S. maltophilia YC has a maximal TCP solubilizing capability when using maltose as carbon source and ammonium nitrate as nitrogen source, respectively, in NBRIP growth medium.

New host and geographic records of five pleosporalean hyphomycetes associated with Musa spp.(Banana)

A study was undertaken to collect and identify saprobic fungi associated with Musa spp.(banana)from Taiwan(China),and Thailand.Samples were collected during the dry season and their morpho-molecular relationships were investigated.Five brown pleosporalean hyphomycetous taxa in Periconiaceae and Torulaceae viz.Periconia cortaderiae,P.delonicis,Torula chromolaenae,T.fici,and T.masonii were identified for the first time from Musa spp.(Musaceae).Phylogenetic analyses of a combined SSU,LSU,ITS,RPB2 and TEF DNA sequence dataset further justified the taxonomic placements of these five taxa in the above mentioned families.Periconia delonicis is reported for the first time on a monocotyledonous host and T.masonii is the first geographical record from Taiwan(China).

Characteristics of heavy metals in soil of lead-zinc mining areas and changes of antioxidant enzyme systems in maize leaf under Pb stress

Pb,Cu,Cd,Zn content of soil in mining areas and abandoned land,flats of the Pijiang River and farmlands were inves-tigated.On this basis of soil heavy metal pollution,the changes of antioxidant enzyme system in maize(Qiandan 88)under different Pb concentrations(0,20,40,60,80,100,150,200,500,1000,2000,3000 mg/L)stress were studied.The results show that the content of Pb,Cu,Cd,and Zn in soil is the highest in mining areas and abandoned land,followed by flats of the Pijiang River>farmlands,and that the variation range of Pb,Cu,Cd in mining areas and abandoned land are 106.40-2564.72,14.83-490.88,22.57-712.77 mg/kg,respectively,which are higher than that of the other land use types.When maize is under stress of 20-500 mg/L Pb concentration,T-SOD activity of maize leaves increase with the increase of Pb concentration and the highest value is 50.21 U/mg prot,but under Pb concentration>1000 mg/L stress,T-SOD activity of maize leaves decrease gradually.The activity of POD decreases with the increases of Pb concentra-tion,and the lowest POD activity of leaves in maize with the value of 93.24 U/mg prot is appeared in Pb 1000 mg/L concentration treatment group.MDA content in leaves of maize increases with the increase of the Pb concentration and the highest value is 101.98 nmol/mg prot,then the content of MDA decreases gradually when the Pb concentration is more than 500 mg/L,which indicates that the membrane lipid peroxidation of maize leaves under high concentration of Pb stress is serious and leads to the cell damage.

Study on in situ stress testing method based on Kaiser effect of acoustic emission and COMSOL simulation

In situ stress testing can improve the safety and efficiency of coal mining.Identifying the Kaiser effect point is vital for in situ stress calculations;however,the in situ stress calculation is limited by the rock sampling angle.Here,the Kaiser effect point identification theory is established and applied to the Xuyong Coal Mine.Uniaxial compression and acoustic emission experiments were carried out on sandstone with 6 sampling directions.Furthermore,COMSOL simulation is applied to study the in situ stress distribution in the coal mine to verify the calculation accuracy.The results are as follows.1)The failure mode of non-bedded and vertical-bedded rocks is primarily tensile shear failure with obvious brittleness in mechanical and acoustic emission characteristics.Shear slip along the bedding plane is the primary failure mode of inclined-bedded rock.Additional take-off points exist in the AE count curve.2)The Kaiser point identification method based on the variation of AE count curve parametersΔti andτi can effectively calculate the in situ stress.According to the numerical value of Kaiser point and sampling direction,the in situ stress of the conveyor roadway in the Xuyong Coal Mine was calculated asσ1=22.81 MPa,σ2=10.87 MPa andσ3=6.14 MPa.3)By the COMSOL simulation study,it was found that a stress concentration zone of 16.13 MPa exists near the two sides roadway.Compared with the Kaiser effect method,the deviation rates of the three-direction principal stress calculated by COMSOL were all less than 5%.This verifies that the in situ stress calculation by Kaiser effect in this study can be applied to the Xuyong Coal Mine.