Sam Kingman

Microwave heating applications in environmental engineering -- a review

This paper presents a review of microwave heating applications in environmental engineering. A number of areas are assessed, including contaminated soil remediation, waste processing, minerals processing and activated carbon regeneration. Conclusions are presented, which identify the areas of potential commercial development as contaminated soil vitrification, volatile organic compounds (VOC) treatment and recovery, waste sludge processing, mineral ore grinding and carbon in pulp gold recovery. Reasons are detailed why other areas have not seen investment into and implementation of microwave heating technology. These include difficulties associated with the scaling up of laboratory units to industrial capacities and a lack of fundamental data on material dielectric properties. This has meant that commercialisation of microwave heating processes for environmental engineering applications has so far been slow. In fact, commercialisation is only deemed viable when microwave heating offers additional process-specific advantages over conventional methods of heating.

Microwave treatment of minerals-a review

This paper presents a review of the advances in the microwave treatment of minerals from the early stages of development to possibilities for future utilisation. Many different applications are considered, including fundamental heating rate studies, microwave assisted grinding, possible exploitation in the area of extractive metallurgy and also microwave treatment of coal. Conclusions are presented regarding the need for further fundamental and pilot scale data. Further indications of the potential for the commercial exploitation of microwaves within the mineral processing and extractive metallurgical industries have been included.

Modern Microwave Methods in Solid-State Inorganic Materials Chemistry: From Fundamentals to Manufacturing

Chemistry: From Fundamentals to Manufacturing Helen J. Kitchen,† Simon R. Vallance,†,‡ Jennifer L. Kennedy,†,§ Nuria Tapia-Ruiz,† Lucia Carassiti,† Andrew Harrison, A. Gavin Whittaker, Timothy D. Drysdale, Samuel W. Kingman,‡ and Duncan H. Gregory*,† †WestCHEM, School of Chemistry, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, United Kingdom ‡Department of Chemical and Environmental Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom School of Engineering, University of Glasgow, James Watt South Building, Glasgow G12 8QQ, United Kingdom Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, F 38042, Grenoble, Cedex 9, France Tan Delta Microwaves Limited, 7 Nettlingflat, Heriot EH38 5YF, United Kingdom

The influence of mineralogy on microwave assisted grinding

The influence of mineralogy on microwave assisted grinding is elucidated. Detailed mineralogical analysis of various commercially exploited ores was carried out and the textural relationships between the individual mineral phases established. Microwave heating profiles were determined for each constituent mineral. Each ore was then subjected to microwave radiation for varying time periods, and change in work index with microwave exposure time quantified. It is suggested that increases in grindability of ores after microwave treatment are related to the specific mineral species present, particle size of the specific mineral and also the degree of dissemination. Conclusions are made regarding the economic implementation of this technology.

Recent developments in microwave processing of minerals

Abstract The demand for minerals and metals is increasing. However, it is well established that the impact of mining and subsequent processing operations must be reduced to meet future sustainability requirements. One way in which mining operations may reduce their impact is through the use of emerging science and technology. One such area which has shown particular promise over a period of several years is the use of microwave heating technologies to improve the efficiency of various mineral processing unit operations including: leaching, refractory gold ore treatment, grindability and liberation and coal grinding. Each of the above areas is reviewed and the main reasons that have either ensured or hindered development to a pilot or industrial scale are discussed. Opportunities for the future development of microwave technologies for the minerals industry are discussed and the review concludes by identifying a series of research challenges that must be met before scale up to an industrial level can be considered.

Application of numerical modelling for prediction of the influence of power density on microwave-assisted breakage

Abstract The influence of electric field strength on the microwave treatment of ore is elucidated. The ore consisted of a microwave-absorbing mineral in a low-absorbing matrix, and the influence of electric field strength was assessed by numerical simulation. Simulations were undertaken using finite difference modelling techniques for a theoretical 15×30 mm sample of calcite host rock containing 10 vol.%, 1-mm2 particles of pyrite. The simulations modelled the microwave heating, thermal conduction, expansion, thermally induced fracturing and strain softening and, finally, uniaxial compressive strength to predict the effect of microwave heating on the strength of the ore material. Standard correlations were then used to develop specific comminution energy verses t10 relationships for the treated and nontreated samples. It is shown that microwave power density is vital to the fracturing of the rock, and it is suggested that by utilising high power densities, the microwave fracturing of rock to reduce grinding energy requirements may be economically viable.

The effect of microwave radiation upon the processing of Neves Corvo copper ore

An investigation into the effect of microwave radiation on the processing of a massive sulphide copper ore has been carried out. It is shown that significant reductions in the Bond work index can be achieved without any discernible adverse effect on the subsequent flotation process. A maximum reduction in work index of 70% was achieved after microwave exposure for 90 s. Microwave exposure followed by water quenching is shown to reduce the work index by up to 15% more than for unquenched samples. Initial trials on the effect of mass loading on the reduction in work index indicate that there exists an optimum mass of material that can be pretreated effectively by microwave radiation in any microwave cavity. Process simulation on the package USIMPAC showed significant flowsheet changes are possible as a result of exposure to microwave radiation and the subsequent reduction in work index. Conclusions are made regarding the economic implications of microwave pretreatment on the flowsheet.

Characterisation of the cross sectional particle concentration distribution in horizontal dilute flow conveying—a review

Abstract This paper presents a review and analysis of the results of recent research that has been carried out on horizontal pneumatic conveying of materials in the dilute phase. An introduction to dilute phase pneumatic conveying is given. Many in-process applications require a detailed knowledge of the cross-sectional particle concentration distribution and an insight into the research carried out in that field is reviewed. Tomography and computational fluid dynamics (CFD) modelling have been identified as the available tools for achieving the aims of such a study and an overview of each is presented. Recent research has concentrated on identifying the optimum operating conditions to increase the energy efficiency of the systems and reducing pipe wear. A developing research area has been the modelling of particle behaviour within pipe systems, especially after bends. Gravitational settling in horizontal pipes, inertial behaviour in pipe bends and branches, turbulent dispersion, turbophoresis and transverse lift forces induced by particle rotation were reported to be the effects governing particle motion that ought to be accounted for by a dilute gas-particle flow model. Particle size, solids loading ratio, pipe material and bend characteristics were identified to be the controllable parameters that determine cross-sectional particle concentration distribution. The effect of secondary turbulent flows and lift forces are enhanced by wall roughness and particle–wall interactions. A new technique of swirling flow pneumatic conveying (SFPC) has been recently applied. However, numerical modelling of such flows is still at an early stage because the mutual coupling between the two phases is not well understood. The physical understanding and modelling of the cross sectional distribution of particles in dilute SFPC has been identified as a challenging area for future research.

Microwave treatment of electric arc furnace dust with PVC: Dielectric characterization and pyrolysis-leaching

Microwave treatment of electric arc furnace dust (EAFD) with poly(vinyl chloride) (PVC) was studied in this work. A comprehensive characterization of the dust as well as assessing the suitability of using the thermal de-chlorination of the common plastic (PVC) under inert atmosphere was carried out to assess the possibility of Zn and other heavy metals extraction (Pb and Cd) from EAFD. The dielectric and thermal properties of EAFD, PVC and their mixtures were measured. Once combined and heated the metal oxides present in the dust reacted with HCl released from PVC during thermal de-chlorination, forming metal chlorides which were subsequently recovered by leaching with water. It was found that zinc chloride could be almost completely recovered in the leaching stage, with the overall recovery of Zn reaching 97% when the EAFD:PVC ratio was 1:2. The investigation highlighted that franklinite, the most refractory mineral to leaching, was completely destroyed. The leaching residue was found to compose mainly of magnetite and hematite.

A new method for determining the optimum dispersant concentration in aqueous grinding

The use of electroacoustics as a method for determining the optimum dispersant dosage for the ultrafine grinding of limestone is presented. The technique measures the zeta potential of concentrated suspensions, hence it was possible to study the adsorption of three commercially available polyelectrolyte dispersants onto the limestone. The optimum dosage of the dispersants was determined and the most suitable one chosen for the grinding experiments. By utilising this optimum dispersant dosage, the productivity and throughput of a stirred vertical mill was greatly enhanced.