Volume 37, Issue 8

Coal fly ash (CFA), an industrial by-product of high-temperature combustion of coal in coal-fired power plants, is one of the most complex and largest amounts of industrial solid wastes generated in China. It is widely recognized that CFA should be considered as a potential alumina resource to substitute bauxite. In this review, the features of high-alumina fly ash and aluminum recovery technologies are first described. Later, the merits and drawbacks of alumina extraction technologies in recovering more valuable materials are compared in terms of extraction mechanisms and equipment requirements. It is shown that “predesilicating-sodium carbonate (Na 2 CO 3 ) activation-acid leaching” is currently a promising method in achieving multimetal synergistic extraction. Finally, the hydrochloric acid and sulfuric acid combination process is proposed as a sustainable development of the predesilicating-Na 2 CO 3 activation-acid leaching process. The findings of this review provide theoretical guidance for novel developments and applications of aluminum extraction technologies.

Rice husk natural fiber remains a highly abundant, eco-friendly and low-cost reinforcement filler for plastic composites fabrication. Hampered by its low aspect ratio and incompatibility with non-polar polymers, its utilization in reinforcing polymer composites often results in decreased composite properties such as decreased tensile strength, impact strength, percentage elongation, and flexural strength. However, stiffness increases. Various surface treatment techniques such as mercerization, compatibilization, acetylation, electron beam irradiation and plasma surface modification have been employed to improve its compatibility with non-polar matrix polymers. This article critically reviews the influence of these surface modification techniques on the resulting composite properties. Based on the analysis of reinforcing efficiencies of these techniques, their strengths, weaknesses, opportunities, and threats, the authors, therefore, project plasma treatment as the most efficient and eco-friendly technique with prospects for high technological application of rice husk plastic composites.

Carbon capture, utilisation, and storage (CCUS) is considered as the least cost-intensive option towards achieving the emission reduction target by 2050. One of the important technologies to remove CO 2 from different gas streams is solvent-based CO 2 capture. Modelling and simulation of solvent-based CO 2 capture processes have been attracting a lot of attention in recent years. Thermodynamic models play a vital role in these modelling and simulation studies. Hence, this study critically reviews the thermodynamic models applied in the modelling of solvent-based CO 2 capture systems over the past years, to provide a guideline for the selection of the optimum models for future studies. These models have wide applications in two main areas: equilibrium modelling [vapour-liquid equilibrium (VLE) (physical) and speciation equilibrium (chemical)], and calculation of some thermodynamic properties. VLE and speciation modelling methods are classified rigorously. VLE modelling methods are classified as homogeneous, heterogeneous, and empirical, and speciation modelling methods are classified as iterative (which could be stoichiometric and non-stoichiometric) and non-iterative. Thermodynamic models are categorised into three key families: activity-coefficient based, equation of state based, and quantum mechanical based. Theory and concepts of different thermodynamic models are presented. Some selected studies that used each family of thermodynamic models are reviewed.

Today, the need of replacing synthetic polymers in the membrane preparation for diverse pervaporation (PV) applications has been recognized collectively and scientifically. Chitosan (CS), a bio-polymer, has been studied and proposed to achieve this goal especially in specific azeotropic water-organic, organic-water, and organic-organic separations, as well as in assisting specific processes (e.g. seawater desalination and chemical reactions). Different concepts of CS-based membranes have been developed, which include material blending and composite and mixed matrix membranes which have been tested for different separations. Hereby, the goal of this review is to provide a critical overview of the ongoing CS-based membrane developments, paying a special attention to the most relevant findings and results in the field. Furthermore, future trends of CS-based membranes in PV technology are presented, as well as concluding remarks and suggested strategies for the new scientist in the field.