Preservation efficiency of new cryoprotectant used for Acidithiobacillus ferrooxidans in liquid nitrogen

The efficiency of a new cryoprotectant,GP,for the preservation of Acidithiobacillus ferrooxidans（A.ferrooxidans） strain DC in liquid nitrogen was investigated.The optimal concentration of this new cryoprotectant for the maximal viable cell recovery and the highest ferrous ion oxidation activity was determined.The results show that 30%（volume fraction） GP is optimal for the cryopreservation with 84.4% of cells surviving,completely oxidizing ferrous ions within 120 h,and growing to a final density of 5.8×107 cell/mL after 6 d in the culture.Furthermore,the optimal residual GP concentration for viable cell recovery after culture of thawed cells in 9K medium for 6 d is 0.6%（volume fraction）.At this concentration,strain DC completely oxidizes ferrous ions within 108 h and grows to a final cell density of 6.8×107 mL-1.Thus,GP is a simple,effective cryoprotectant for the preservation of A.ferrooxidans strain DC in liquid nitrogen.

Rock mechanical properties of coal in cryogenic condition

Liquid nitrogen(LN2)fracturing is a kind of non-aqueous fracturing technology,which is expected to provide a new and efficient way for coalbed methane(CBM)development.The mechanical properties of coal under LN_(2) freezing are very important for studying the mechanism of LN2 fracturing.However,most of the current research is limited to studying mechanical properties of rocks after being frozen by LN2 and returned to room temperature.In this paper,the effect of LN2 freezing on the mechanical properties of coal was studied.Uniaxial strength tests and Brazil tests were carried out for dry and water-saturated coal samples with different types and bedding directions.In addition,standard electron microscopy(standard SEM)and cryo-electron microscopy(Cryo-SEM)were used to compare the fracture morphology of coal samples at room temperature and LN_(2) temperature.The results showed that LN_(2) freezing can damage and improve the mechanical properties of coal simultaneously.The strength of saturated coal under freezing is higher than that of dry coal,and the filling of ice can enhance the mechanical strength of coal.In addition,the mechanical properties of coal with higher porosity are enhanced more than that of coal with lower porosity under LN_(2) freezing.The main findings of this study are the keys to the research of LN_(2) fracturing mechanisms in CBM reservoirs.