Review of coal and gas outburst in Australian underground coal mines

Outburst of coal and gas represents a significant risk to the health and safety of mine personnel working in development and longwall production face areas. There have been over 878 outburst events recorded in twenty-two Australian underground coal mines. Most outburst incidents have been associated with abnormal geological conditions.Details of Australian outburst incidents and mining experience in conditions where gas content was above current threshold levels are presented and discussed. Mining experience suggests that for gas content below 9.0 m³/t, mining in carbon dioxide (CO₂) rich seam gas conditions does not pose a greater risk of outburst than mining in CH₄ rich seam gas conditions. Mining experience also suggests that where no abnormal geological structures are present that mining in areas with gas content greater than the current accepted threshold levels can be undertaken with no discernible increase in outburst risk. The current approach to determining gas content threshold limits in Australian mines has been effective in preventing injury from outburst, however operational experience suggests the current method is overly conservative and in some cases the threshold limits are low to the point that they provide no significant reduction in outburst risk. Other factors that affect outburst risk, such as gas pressure, coal toughness and stress and geological structures are presently not incorporated into outburst threshold limits adopted in Australian mines. These factors and the development of an outburst risk index applicable to Australian underground coal mining conditions are the subject of ongoing research.     

Application of 'waste' metal hydroxide sludge for adsorption of azo reactive dyes

The capacity and mechanism of metal hydroxide sludge in removing azo reactive dyes from aqueous solution was investigated with different parameters, such as charge amount of dyes, system pH, adsorbent particle size, and adsorbent dosage. The three anionic dyes used were CI Reactive Red 2, CI Reactive Red 120, and CI Reactive Red 141, increasing in number of sulfonic groups, respectively. Only 0.2% (w/v) of powdered sludge (<75microm) achieved color removal from 30 mg l(-1) reactive dye solutions within 5 min without pH adjustment. The larger the charge amount of the dyes, the greater the adsorption (>90%) on the metal hydroxide sludge. The system pH played a significant role in the adsorption on metal hydroxides and formation of dye-metal complexes. The optimum system pH for dye adsorption was 8-9 which was close to the pH(zpc) of the sludge while the precipitation of dye-metal complexes occurred at system pH 2. The maximum adsorption capacity (Q degrees ) of the sludge for the reactive dyes was 48-62 mg dye g(-1) adsorbent. The Langmuir and Freundlich models showed that the higher charged dyes had a higher affinity of adsorption. The smaller particle size and the greater amount of adsorbent showed the faster process, due to an increase in surface area of adsorbent. Desorption studies elucidated that metal hydroxide sludge had a tendency for ion exchange adsorption of sulfonated azo reactive dyes. Leaching data showed that the treated water was nontoxic at a system pH above 5 or a solution pH above 2.     

Treatment of oily waters using vermiculite

The main objective of this study was to examine the removal of oil from water by expanded and hydrophobized vermiculite. A pH of 9 showed a higher removal efficiency of oil by vermiculite. Oil removal efficiencies at pH 9 were found to be 79%, 93%, 90%, 57% for standard mineral oil (SMO), Canola oil (CO), Kutwell oil (KUT45), refinery effluent (RE), respectively, in the case of expanded vermiculite, and 56%, 58%, 47%, 43% for SMO, CO, KUT45 and RE, respectively, for hydrophobized vermiculite. Kinetic data satisfied both the Lagergren and Ho models. Equilibrium studies showed that the Langmuir isotherm was the best-fit isotherm for oil removal by both expanded and hydrophobized vermiculite. The data showed a higher adsorptive capacity by the expanded vermiculite compared to the hydrophobized vermiculite. Desorption studies showed that the expanded vermiculite did not desorb oil to the same extent compared to hydrophobized vermiculite. The Freundlich isotherm was the best-fit model for desorption. Expanded vermiculite showed better retention than hydrophobic vermiculite. The results showed that the expanded vermiculite had a greater affinity for oil than hydrophobized vermiculite.     

Adsorption and desorption characteristics of mercury(II) ions using aminated chitosan bead

Adsorption and desorption characteristics for mercury ions using aminated chitosan bead which showed very high affinity to mercury ions were studied. The adsorption of mercury ions using aminated chitosan bead was an exothermic process since binding strength each other increased as the temperature decreased. And the adsorption of mercury ions was almost completed in 100 min at 150 rpm. In case that adsorbent dose increased, mercury uptake capacity decreased, while, removal efficiency increased. The beads were not greatly affected by the ionic strength, organic material and alkaline-earth metal ions. Mercury ions adsorbed on aminated chitosan bead were desorbed effectively about 95% by EDTA and the adsorption capacity of the recycled beads can still be maintained at 90% level at the 5th cycle.     

Sorbed atrazine shifts into non-desorbable sites of soil organic matter during aging

Soil-chemical contact time (aging) is an important determinant of the sorption and desorption characteristics of the organic contaminants and pesticides in the environment. The effects of aging on mechanism-specific sorption and desorption of atrazine were studied in soil and clay slurries. Sorption isotherm and desorption kinetic experiments were performed, and soil-water distribution coefficients and desorption rate parameters were evaluated using linear and non-linear sorption equations and a three-site desorption model, respectively. Aging time for sorption of atrazine in sterilized soil and clay slurries ranged from 2 days to 8 months. Atrazine sorption isotherms were nearly linear (r(2)>0.97) and sorption coefficients were strongly correlated to soil organic carbon content. Sorption distribution coefficients (K(d)) increased with increase in age in all five soils studied, but not for K-montmorillonite. Sorption non-linearity did not increase with increase in age except for the Houghton muck soil. Desorption profiles were well described by the three-site desorption model. The equilibrium site fraction (f(eq)) decreased and the non-desorbable site fraction (f(nd)) increased as a function of aging time in all soils. For K-montmorillonite, f(nd) approximately 0 regardless of aging, showing that aging phenomena are sorbent/mechanism specific. In all soils, it was found that when normalized to soil organic matter content, the concentration of atrazine in desorbable sites was relatively constant, whereas that in non-desorbable site increased. This, and the lack of aging effects on desorption from montmorillonite, suggests that sorption into non-desorbable sites of soil organic matter is primary source of increased atrazine sorption in soils during aging.     

Desorption and re-adsorption of carbon nanotubes: comparisons of sodium hydroxide and microwave irradiation processes

This study evaluates exhausted carbon nanotubes regenerated by desorption processes using 1mM NaOH and microwave irradiation processes. Kinetic analyses of re-adsorption were performed using pseudo first- and second-order models. Regression results revealed that a pseudo first-order model accurately captured re-adsorption kinetics. The regeneration efficiency was 28, 30, 35 and 44% at 18, 28, 38 and 48 degrees C using desorption agent of 1mM NaOH for 24h, respectively. Microwave power was considered the most important factor in regeneration experiments, as the temperature reached by exhausted CNTs was directly related to microwave power in this study. Additionally, microwave regeneration was more effective than the desorption agent of NaOH. The most effective conditions for regenerating exhausted CNTs were a microwave power input of 1000 W for 20 min.     

超声波作用下的煤层气吸附-解吸规律实验

目前,对于超声波作用下的煤层气吸附-解吸规律及超声波促进煤层气解吸机理的研究还有待于进一步深入。为此, 利用自行设计的实验平台,开展了超声波作用下的煤样等温吸附-解吸实验（实验煤样采自山西晋城成庄煤矿和高平建业煤矿的下 二叠统山西组15 号煤层）。实验结果显示,未加载超声波时,伴随着压力的逐渐增大,煤样对CH₄ 的吸附量逐渐增加;但在加载 超声波后,随着超声波功率的增大,煤样的吸附能力逐渐减弱,且随着系统压力的释放,煤样的解吸速率逐步增大。超声波使得煤 样吸附能力降低的原因主要在于：①超声波的热效应使得煤样内部温度升高,降低了煤样的吸附能力;②煤岩表面势能的提高以及 超声波作用下色散力的产生,使得CH₄ 气体分子被吸附的概率降低。而煤样解吸速率增大的原因可解释为：在施加超声波的情况下, 煤体内部质点发生微位移并产生新的裂隙、微裂隙和孔隙,从而促进了煤层气的解吸和扩散。结论认为：超声波功率与煤样Langmuir 常数呈负相关关系,利用所得到的实验数据可以拟合Langmuir 常数与超声波功率之间的函数关系,据此可建立超声波与煤岩 吸附特性之间的数值关系。     

Laboratory investigation of a new scale inhibitor for preventing calcium carbonate precipitation in oil reservoirs and production equipment

The formation of mineral scale is a complex problem during the oilfield operations. Scale inhibitors are widely used to prevent salt precipitation within reservoirs, in downhole equipment, and in production facilities. The scale inhibitors not only must have high effectiveness to prevent scale formation, but also have good adsorption–desorption characteristics, which determine the operation duration of the scale inhibitors. This work is focused on the development of a new scale inhibitor for preventing calcium carbonate formation in three different synthetic formation waters. Scale inhibition efficiency, optical density of the solution, induction time of calcium carbonate formation, corrosion activity, and adsorption–desorption ability were investigated for the developed scale inhibitor. The optimum concentration of hydrochloric acid in the inhibitor was determined by surface tension measurement on the boundary layer between oil and the aqueous scale inhibitor solution. The results show that the optimum mass percentage of 5 % hydrochloric acid solution in the inhibitor was in the range of 8 % to 10 %. The new scale inhibitor had high efficiency at a concentration of 30 mg/L. The results indicate that the induction period for calcium carbonate nucleation in the presence of the new inhibitor was about 3.5 times longer than the value in the absence of the inhibitors. During the desorption process at reservoir conditions, the number of pore volumes injected into the carbonate core for the developed inhibitor was significantly greater than the volume of a tested industrial inhibitor, showing better adsorption/desorption capacity.     

Thermal treatment of petroleum contaminated soils by a fluidized bed desorber

A novel type of fluidized bed desorber was developed for the remediation of petroleum-contaminated soils at low temperature with high efficiency. The performance of the fluidized bed desorber was experimentally investigated in two different operation modes. Results of continuous operation of fluidized bed indicated that the effect of the mass ratio of the fluidizing gas flow rate to the feed rate of contaminated soil was not significant at temperatures above 300 ‡C as long as proper fluidization was ensured. Periodic fluidization mode was tested aiming at reduction of off-gas volume. Effects of cycle time and split fraction on desorption efficiency were investigated. Within the range of experimental conditions, desorption efficiency decreased with increase of cycle time and split due to defluidization in the bed. With suitable choice of cycle time and split, periodic fluidization of the desorber enabled considerable reduction of off-gas volume without compromising desorption efficiency.