The use of vertical stirred mills in the mining industry has increased remarkably over the past few decades as a result of the growing demand for finer ore grinding. This equipment is recognized to deliver higher energy efficiency in fine grinding operations when compared to conventional tubular mills. Methods of designing vertical stirred mills involve operational experience, pilot plant tests and bench tests. An important issue is that the laboratory-scale test, conducted in the standard 8"×10" jar, requires at least 10–20 kg of material, depending on ore density, which is not available in many cases, particularly in the early stages of greenfield projects. For regrinding of flotation concentrates, several bench scale flotation tests are required to generate such a sample. The paper describes the development and validation with six different ore samples of a simplified laboratory jar mill test using a 6"×8" jar, which is smaller than the 8"×10" size, the latter commonly used which requires about one-tenth of the mass required in the standard test. The proposed test indicated similar results as compared to the standard procedure.
Unwanted changes in powder flow behavior can unexpectedly occur when a product is exposed to certain conditions of temperature and humidity. This can happen during production, but also during transport or storage. The work reported here demonstrates the novel approach of using an amended powder rheology set-up for measuring and predicting such changes in powder flow behavior. The developed methodology makes it possible to vary in-situ the temperature and the relative humidity of the air to which the product is exposed, thereby mimicking realistic conditions of production or related unit operations. An air flow capable of fluidizing the powder particles is controlled at a specific constant temperature and its relative humidity can be altered while measuring the torque in the fluidized powder bed in real time. The fluidization is necessary for generating a homogeneous introduction of temperature and relative humidity. Results obtained using citric acid and commercial coffee whitener products have proven this methodology to provide both similar and in certain instances dissimilar results compared to the more established methodology such as measuring the vapour adsorption isotherms. These observations are explained. In this way, it can be predicted under which combinations of temperature and humidity a product does or does not become sticky. The main advantages of our approach are that the flow properties are directly assessed, the interpretation of the obtained data is more straightforward and that the measurement times are shortened substantially.
Microorganisms are ubiquitous in the environment. Wherever their sources are present, the particles can be released into the air forming microbiological aerosols. Although most of their particles cause no harm to the exposed individuals, some of their propagules may have infectious or allergenic potential and may carry toxic or irritant substances and components. Their inhalation usually poses a significant health risk and is responsible for numerous adverse outcomes, from allergic reactions, infections and toxic responses to various nonspecific symptoms. This review article provides fundamental background information on the role of microorganisms in the environment, defines and characterizes environmental sources of microbial aerosols, describes microbial abilities for airborne transport and comments on their role in atmospheric processes, discusses their physical and biological characteristics which result in adverse health outcomes observed in exposed individuals. The paper characterizes comprehensively numerous sampling and analysis techniques involved in the quantitative and qualitative evaluation of microbial aerosols together with their practical applications, presents strategies applied in the assessment of harmful microbial agents formed by bioaerosols, explains the ways of creating hygienic standards (understood here as reference/threshold limits) for microbiological aerosols conditioned by both medical and environmental determinants, and comments on their usefulness in the control and protection of environment and health.
A continuous flow reaction process in which a metal salt solution is rapidly mixed with high-temperature water was employed to achieve rapid heating up to supercritical conditions. A quarter of a century has passed since the supercritical hydrothermal method was first proposed. This paper introduces recent advances in science and technology related to the supercritical process. Process design, kinetics, reaction atmosphere (redox) control, morphology control, organic modification of particles, nanocatalysts, and organic-inorganic hybrid materials are reviewed for promising applications of the supercritical process.
Optical Coherence Tomography (OCT) is a light-based imaging method capable of simultaneously capturing the internal structure and motion (1D, 2D or 3D) of various opaque and turbid materials with a micron-level spatial resolution. Depending on the OCT technology, axial scanning rates can vary in a range of tens to hundreds of kHz. The actual imaging depth significantly depends on the optical properties of the material and can vary from micrometers to a few millimeters. From the viewpoint of industrial applications, OCT technology is very appealing. Due to its resolution, speed, and ability to deal with opaque materials, it fills an apparent gap in available measurement methods. Nonetheless, OCT has not to date seen widespread growth in the industrial field. This has been at least partly due to a lack of commercial devices compact and flexible enough to adapt to industrial needs. The recent emergence of more generic commercial OCT devices has considerably lowered the threshold for adapting the technique. The utilization of OCT for structural analysis, also outside the medical field, has been thoroughly discussed in scientific literature. Therefore, in this paper, we will mainly concentrate on applications of OCT that also utilize its capability of performing velocity measurements. The emphasis will be on industrially motivated problems such as rheology, microfluidics, fouling and turbulence.
Classic crystallization describes a burst nucleation followed by a layer-by-layer atom deposition. The non-classic crystallization refers to particle mediated crystallization process. Different crystallization routes lead to the formation of diverse structured materials. Here we report a rational synthesis of silver particles by selecting the crystallization routes. Silver particles were synthesized by a solution reduction approach. The crystallization routes were regulated by adding amino acids to stabilize silver ions which leads to the decrease of the reduction rate. Without amino acids, silver dendrites were largely formed. With the addition of amino acids, flower-like (low concentration of amino acids) and spherical silver (high concentration of amino acid) particles were synthesized. Three kinds of amino acids were tested and the similar results were obtained. The time-dependent characterization on the evolution of silver particles showed that silver dendrites were formed by the classic atom deposition while the other two morphologies were formed by the combination of classic and non-classic crystallization. The silver particles synthesized were evaluated for ethylene epoxidation and the dendritic particles demonstrated a high selectivity.
There is an increasing demand of air filters with a high collection performance, i.e., high collection efficiency and low pressure drop, for the application to indoor air cleaning. Air filters consisting of nanofibers have attracted great interests since they may have a low pressure drop because of slip flow effect and high collection efficiency due to enhanced interception effect. Although various nanofiber filters are available on the market, their collection performance is not as high as expected by the conventional filtration theory because non-uniform packing of fibers plays a significant role in the nanofiber filtration. In the present review, the present status of development of high performance air filters are reviewed. We may use air filters not only for the removal of particles but also for the classification of particles by selecting an appropriate filter by operating it under an optimized filtration condition for classification. Other topics introduced in the present review are the applications of filters and metal screen for aerosol classification and the use of centrifugal force for enhancing collection efficiency without increasing the pressure drop.