Heechan Cho

Biodegradability and biodegradation rate of poly(caprolactone)-starch blend and poly(butylene succinate) biodegradable polymer under aerobic and anaerobic environment

The biodegradability and the biodegradation rate of two kinds biodegradable polymers; poly(caprolactone) (PCL)-starch blend and poly(butylene succinate) (PBS), were investigated under both aerobic and anaerobic conditions. PCL-starch blend was easily degraded, with 88% biodegradability in 44 days under aerobic conditions, and showed a biodegradation rate of 0.07 day(-1), whereas the biodegradability of PBS was only 31% in 80 days under the same conditions, with a biodegradation rate of 0.01 day(-1). Anaerobic bacteria degraded well PCL-starch blend (i.e., 83% biodegradability for 139 days); however, its biodegradation rate was relatively slow (6.1 mL CH(4)/g-VS day) compared to that of cellulose (13.5 mL CH(4)/g-VS day), which was used as a reference material. The PBS was barely degraded under anaerobic conditions, with only 2% biodegradability in 100 days. These results were consistent with the visual changes and FE-SEM images of the two biodegradable polymers after the landfill burial test, showing that only PCL-starch blend had various sized pinholes on the surface due to attack by microorganisms. This result may be use in deciding suitable final disposal approaches of different types of biodegradable polymers in the future.

The modeling of dry grinding of quartz in tumbling media mills

Abstract The grinding of quartz sand to produce high purity silica flour was studied using ceramic balls, ceramic cylinders or flint pebbles in a laboratory mill and three full-scale closed circuit mills of 2.2, 2.3 and 2.8 m internal diameter. The primary breakage distribution determined in laboratory tests was the same for the three media types but the characteristic slope (γ) was changed from 1.05 to 0.95 to fit the full-scale results. An approximate correction was used for non-first order breakage kinetics. Simulation models were developed for the air separator and the mills. Simulations indicated that a mill lining of smooth ceramic gave media slip and was less efficient than flint linings. Higher circulating loads reduced specific grinding energy even though the recycle of fine mill product to mill feed increased. Ceramic balls gave the lowest grinding energy, wear rate and cost per ton of product.

Fine grinding of aggregated powders

In many cases, including natural ores as well as synthetic powders, fine grinding involves the breakage of bound aggregates rather than solid particles. The characteristics of breakage in such systems have been investigated by experimental studies of grinding kinetics, in a model system of partially sintered alumina particles, ground in a laboratory centrifugal ball mill. The effects of aggregate strength (extent of sintering) and energy input (mill speed) on the breakage rates and breakage distributions have been evaluated. Breakage appears to occur primarily through splitting of the aggregated mass into two or three smaller aggregates accompanied by release of the primary particles, leading to strongly bimodal breakage distributions.

An alternative method for programming mill models

Abstract It is shown that the simple algebraic equation set that describes the breakage rate-mass (population) balance in a fully mixed grinding mill operating at steady state is readily extended to describe mills with other residence time distributions. The algorithms are simple to program as they do not require the use of the Reid solution to the batch grinding set, and they compute rapidly. The formulation is particularly useful for the large diameter–short length semiautogenous tumbling mills that have residence time distributions close to those expected for a fully mixed system. Examples are given using the complex form of the specific breakage function that is applicable to this type of mill. The algorithms are suitable for the direct applications of the Austin method of allowance for different particle velocities in a mill as a function of particle size.

The equivalence between different residence time distribution models in ball milling

Abstract A number of different models have been used to describe the residence time distributions (RTDs) measured for dry and wet ball milling by various investigators in various countries. It is useful to be able to compare the results between different workers and this requires a knowledge of the equivalence of the models. A method is presented here that permits this comparison for the usual two parameter residence time distribution models, where one parameter is the mean residence time and the other is a characteristic parameter that defines the shape of the residence time distribution. The method defines the best correlation as that which produces the closest agreement of the predicted mill product size distributions over a wide range of values of mean residence time. The correlations are given in graphical form and in equation form. In some circumstances simulation results are not sensitive to the RTD model chosen, provided that the correct match of characteristic parameters is used.

An equation for the breakage of particles under impact

Abstract Using data from the literature, the following simple empirical equation is derived for the cumulative mass fraction of particles broken (m) when impacted at a specific impact energy (J/g of impacted mass) of E: m i (E)= 0 , E≤E min i A ln (E/K i ), E min i ≤E≤E max i 1, E≥E max i where E min i =K i E max i =K i exp (1/ A ) and K i =C(x i /x o ) −m . In this equation, i is an integer index of a √2 screen size interval of upper size xi; xo is a standard size of 1 mm; Emini is the minimum specific impact energy required to produce significant breakage of feed material of size i and Emaxi is the specific impact energy that breaks all feed material of size i. Ā, C and m are material-dependent constants. Values of Ā=0.235, m=0.58 and C=0.13 J/g were found for particles of limestone in a thin bed impacted by a falling steel ball. The equation shows that smaller particles require a higher specific impact energy than larger particles to give the same fraction of breakage out of the feed size interval.

Coal and solvent properties and their correlation with extraction yield under mild conditions

Coal solvent extraction is a clean coal technology that involves the extraction of organic matter from coal using solvents. In this study, the effects of various coal and solvent properties on extraction yield were studied and their correlations were observed. Solvent extraction was performed for fifteen coal samples of different ranks with eight solvents under mild conditions. Statistical analyses were then conducted to find correlations between the extraction yields and the coal and solvent characteristics. The extraction yield was strongly correlated with the atomic H/C ratio or volatile matter content. Among the solvent properties, the correlation between the electron donor, acceptor number (DN-AN) and yield was confirmed to be high. The results of multiple regression showed that positive correlations were found with the content of volatile matter of coal and polar force, DN-AN of solvent. Whereas negative correlations were found with the Ca/Mg content of coal and dispersion force, hydrogen bonding force of solvent. The regressionequation- calculated value was similar to the experimental value.

Identification of Calcium Sulphoaluminate Formation between Alunite and Limestone.

This study was carried out to identify the conditions of formation of calcium sulphoaluminate (3CaO·3Al2O3·CaSO4) by the sintering of a limestone (CaCO3) and alunite [K2SO4·Al2(SO4)3·4Al(OH)3] mixture with the following reagents: K2SO4, CaCO3, Al(OH)3, CaSO4·2H2O, and SiO2. When K2SO4, CaCO3, Al(OH)3, CaSO4·2H2O were mixed in molar ratios of 1:3:6:3 and sintered at 1,200∼1,300 °C, only 3CaO·3Al2O3·CaSO4 and calcium langbeinite (2CaSO4·K2SO4) were generated. With an amount of CaO that is less than the stoichiometric molar ratio, 3CaO·3Al2O3·CaSO4 was formed and anhydrite (CaSO4) did not react and remained behind. With the amount of CaSO4 that is less than the stoichiometric molar ratio, the amounts of 3CaO·3Al2O3·CaSO4 and 2CaSO4·K2SO4 decreased, and that of CaO·Al2O3 increased. In the K2SO4-CaO-Al2O3-CaSO4-SiO2 system, to stabilize the formation of 3CaO·3Al2O3·CaSO4, 2CaSO4·K2SO4, and β-2CaO·SiO2, the molar ratios of CaO: Al2O3: CaSO4 must be kept at 3:3:1 and that of CaO/SiO2, over 2.0; otherwise, the generated amount of 3CaO·3Al2O3·CaSO4 decreased and that of gehlenite (2CaO·Al2O3·SiO2) with no hydration increased quantitatively. Therefore, if all SO3(g) generated by the thermal decomposition of alunite reacts with CaCO3 (or CaO, the thermal decomposition product of limestone) to form CaSO4 in an alunite- limestone system, 1 mol of pure alunite reacts with 6 mol of limestone to form 1 mol of 3CaO·3Al2O3·CaSO4 and 1 mol of 2CaSO4·K2SO4.

Shredding and liberation characteristics of refrigerators and small appliances

Mechanical disaggregation, or shredding, is an important part of the recycling process. Occurring at the beginning of the processing sequence, it significantly affects the efficiency of downstream processing stages. This study examines the size reduction and liberation characteristics of the single-stage shredding of household appliances to improve the efficiency and quality of the recycling process. Several disposed appliances, including 75L refrigerators and five major categories of small appliances (vacuum cleaners, videocassette recorders (VCRs), electric rice cookers, fans, and electric heaters), were shredded using a high-speed vertical shredder under varying discharge clearance conditions. The fragments were analyzed according to size, composition, and degree of liberation. It was found that single-stage crushing with the high-speed vertical shredder was sufficient to produce fragments at an appropriate size and with a high degree of liberation. Based on the experimental results, an optimal shredding and separation scheme for the process is proposed.

Leaching behavior of U and V from a Korean uranium ore using Na2CO3 and KOH

Leaching behavior of uranium and vanadium from a uranium ore deposit found in Koi-san, Chung-buck Province, Korea has been studied using KOH–Na2CO3. The pH of the solution was controlled to 10, using 1.0 mol/l KOH solution. The effects of the concentration of Na2CO3, temperature, and particle size on the overall leaching behavior were closely investigated and results were very promising. For example, the leaching of U and V was found to be more than 90% and 65%, respectively, at 80°C after 3 h leaching. The activation energy of uranium and vanadium was found to be 7.4 and 7.9 kcal/mol, indicating that both chemical reaction and mass transfer were important in this reaction.