A Review of the Milestones Reached by the Attainable Region Optimisation Technique in Particle Size Reduction

The attainable region (AR) is an optimization method adopted for use in comminution to achieve different objective functions, which all converge to optimising the production of the desired particle size distributions for downstream processes. The technique has so far mostly been used to optimise the breakage of particles in tumbling mills. It achieved the desired purpose by unveiling all possible outcomes derived from a combination of operational parameters that are bound by trajectories showing the limitations of a system. The technique has given the scientific community lenses to see the behaviour of different parameters in ball mills otherwise known as the black boxes due to their concealing nature. Since its inception, the AR technique has been applied to data obtained from the laboratory tests and simulated industrial mills and the results sometimes contradict or confirm the conventional milling practices in the industry. This makes the already conservative mining industry sceptical about its adoption. This review thus assesses the milestone covered as far as the AR development in comminution is concerned. It also helps to clarify the sources of the discrepancies between the AR results and the conventional knowledge concerning the optimisation of ball mill operational parameters.

Gasification of Waste Tyres: Thermodynamic Attainable Region Approach

The innovative G-H graphical technique, a plot of Enthalpy vs Gibbs free energy was utilized to obtain a thermodynamically attainable region (AR) for the gasification of waste tyres. The AR is used to examine the interaction between the competing reactions in a gasifier and used to identify optimal targets for the conversion of waste tyres. The objective is to investigate the effect of temperature on the product selectivity. a temperature range of 25-1500°C at 1 bar was used for the analysis. The results show that at temperatures from 200°C to 600°C methane and carbon dioxide are dominant products at minimum Gibbs free energy. However, as the temperature increases, methane production decreases and hydrogen production become more favourable. Between 600°C and 700°C, carbon dioxide and hydrogen are dominant products. The AR results show that the products of gasification (CO and H2) are preferred products at minimum Gibbs free energy only at temperatures from 800°C to 1500°C, when both water and oxygen are used as oxidants. Therefore, syngas production from tyres is only feasible at high temperatures. Temperatures above 1000°C are recommended to prevent the formation of intermediate radicals.

CO2 Carbonation of Olivine-Admixed Marine Clay: Suitability for Bottom Liner Application

This paper focuses on employing an optimization approach in evaluating the hydraulic conductivity (HC) of CO2-carbonated olivine-admixed marine clay for possible utilization as a hydraulic barrier in engineered landfills to minimize leachate migration. The attainable region technique was used to optimize the olivine particle size during the grinding process before treating the soil, while the response surface methodology was used in designing the experiments, evaluating the results, and optimizing the variables responsible for reducing the HC of the CO2-carbonated olivine-treated clay. The effects of the control factors (olivine content, carbonation time, and carbonation pressure) on the response (HC) were studied by variance analysis. The factors and the response were related by a developed regression model. Predicted values from the model were in concurrence with their experimental counterparts. The results show that the HC of the CO2-carbonated olivine-treated clay samples met the Malaysian regulatory specification of ≤10−8 m/s for liner utilization. The optimum conditions were 24.7% olivine content, 20.1 h carbonation time, and 161 kPa carbonation pressure, which decreased the HC by approximately 98%. CO2-carbonation and olivine blend proved to be a sustainable technique to reduce the clay’s HC for possible application as a liner material in engineered landfills.

Attainable Region Approach in Analyzing the Breakage Behavior of a Bed of Olivine Sand Particles: Optimizing Impact Energy and Particle Size

In this study, we investigated the breakage behavior of a bed of olivine sand particles using a drop-weight impact test, with drop weights of various shapes (oval, cube, and sphere). An Attainable Region (AR) technique, which is a model-free and equipment-independent technique, was then applied to optimize the impact energy during the breakage process and also to get particles in defined particle size classes. The findings revealed that the different drop weights produce products within the three different particle size classes (feed, intermediate, and fine). A higher mass fraction of materials in the fine-sized class (−75 μm) was obtained when the spherical drop weight was used relative to the cubic and oval drop weights. The drop height was found to have a significant influence on the breakage process. The AR technique proved to be a practical approach for optimizing impact energy and particle size during the breakage of a bed of olivine particles, with potential application in sustainable soil stabilization projects.

Cobalt Catalyst Reduction Thermodynamics in Fischer Tropsch: An Attainable Region Approach

A fundamental understanding of the precise reduction reaction pathway of cobalt-based catalysts is a crucial piece of knowledge in terms of the Fischer–Tropsch Synthesis (FTS) reaction. The use of hydrogen (H2) as the reduction agent results in a two-stage reduction of cobalt tetraoxide (Co3O4) to cobalt oxide (CoO) and then to metallic Co. The objective of the present work is to apply the Thermodynamic Attainable Region (TAR) to cobalt catalyst reduction using H2 so as to gain better insight regarding the thermodynamics of reduction reaction. TAR space diagrams suggest that complete Co3O4 reduction is feasible through two reaction pathways. Thus, the observed AR results suggest that the temperature programmed reduction’s (TPR) first reaction peak may be attributed to direct reduction of Co3O4 → Co and/or reduction to an intermediate compound Co3O4 → CoO. The second peak is a result of the reduction of either of the cobalt oxides to Co (Co3O4 → Co or CoO → Co).