Different perspectives of dynamics in comminution processes

The performance of a comminution and classification process depends on the design and configuration of each process unit, the configuration of the plant, the design of the control and physical properties of the incoming feed. Comminution processes should be designed to have a stable and efficient production over a wide range of conditions. However, demands from the management, operational cost, investment, maintenance or any other related field can result in process alterations that are not beneficial for the stability of the circuit and, therefore, utilization and efficiency of the production. Furthermore, advanced process control and optimization rely heavily on understanding the dynamic behaviour of the process in achieving a more stable and consequently efficient process. This review aims to explore different dynamic aspects from particle, bulk, unit and process perspectives, their origin, and what consequences they may have on the operation. The aim is to illustrate a holistic view of process dynamics that should be considered when evaluating circuit performances and identifying risk zones that affect the process, considering the state-state performance and dynamic behaviour. Based on that, several dynamic related issues were formulated and ranked by experts within the field to get a subjective perspective. Issues such as process control design and configuration, ore variability, segregation and upstream disturbances ranked high in possible gains for comminution processes

Texture, liberation and separation modelling of complex ores

Many of the existing liberation models combine a model of texture that describes the intact ore structure with a model of particle production. The Geometric Texture Model (GTM) proposed by the authors calculates particle compositions for describing multi-mineral liberation distributions, but these can also be used to generate particles with representative composition distributions to feed particle-based models of various unit processes. In this paper, a model of a meso-texture from the George Fisher deposit is used in combination with a particle-based model that responds to surface composition of particles to predict the overall flotation response of the ore

The green-agile supplier selection problem for the medical devices: a hybrid fuzzy decision-making approach

The supplier selection problem (SSP) is known as one of the major issues in the supply chain management area. In this field, the literature shows that the combination of green and agile indicators has been ignored by researchers. Hence, this research attempts to study the SSP considering green and agile aspects, simultaneously. To do this, an efficient hybrid fuzzy decision-making approach is developed based on the Fuzzy Decision-Making Trial and Evaluation Laboratory (FDEMATEL), Fuzzy Best-Worst Method (FBWM), Fuzzy Analytic Network Process (FANP), and Fuzzy Vlse Kriterijumsk Optimizacija Kompromisno Resenje (FVIKOR) methods. Then, to show the efficiency and application of the proposed approach, a case study in the medical devices industry is investigated. After determining the main indicators and alternatives, the interrelationships between indicators are identified employing FDEMATEL. Then, the weights of indicators are calculated using integrated FBWM-FANP. Finally, the potential suppliers are ranked applying FVIKOR. Based on the obtained results, price and greenness are the more important aspects and also material costs, environmental performance evaluation, manufacture flexibility, service level, and system reliability are the most important criteria for the green-agile supplier selection problem in the medical devices industry. Since all of the consistency ratios are less than 0.1, the reliability of the results is proved. On the other side, the results of conducting sensitivity analysis show that by changing the defuzzification methods, there is no significant change in the obtained results that demonstrates the validity of the proposed approach. Eventually, based on the obtained results, suppliers #1 and #5 are the best suppliers for the considered company. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11356-021-14690-z

Interpreting low energy attrition behaviour in a pilot mill using numerical modelling

The conditions under which rocks become superficially damaged during the grinding process are not well understood. The main purpose of the work presented here is to understand how superficial breakage occurs under incremental low-energy impacts. To enable this study a series of abrasion tests with multisize pilot mills have been performed. Outcomes of numerical simulation corresponding to each test were examined to investigate the experimental results. Abrasion tests have been conducted using three grinding mill sizes (i.e. 1.8, 1.2, and 0.8 m). Two types of ore were used to investigate different hardness strengths. To ensure abrasion was the dominant mechanism, in all tests the mill speed was reduced to 40% of critical speed. The relationship between the Fractional mass loss rate and particle size was investigated by randomly collecting seven tracer particles from sizes -73+63, -53+45, and -37.5+31.5 mm. It was evident from the results that the Fractional mass loss rate of angular particles declines as the particle size increases whereas the Fractional mass loss rate decreases from fine to coarse in rounded particles. Results of Discrete Element Method (DEM) simulations indicate that fine particles experience higher levels of collision energy per particle and this value reduces as the particle size increases and mill size reduces. This explains the higher Fractional mass loss rate of smaller particles as well as the increase in the Fractional mass loss rate as the mill size increases. Linked DEM and experimental data indicates that under these test conditions surface damage attrition is the dominant mechanism. This work suggests that DEM simulation can be implemented to predict the abrasion wear of particles in mills

Assessment of hydrocyclone operation in gravity induced stirred mill circuit

The performance data of hydrocyclones in circuits containing a gravity induced mill (hereafter referred to as a stirred mill) were evaluated to understand their performance in the circuits and the current operational practices. There are many studies conducted to understand and evaluate the hydrocyclone performances in the semi-autogenous mill (SAG) and ball mill circuits. The literature on hydrocyclone operation in stirred milling circuits is still limited. A database consisting of various hydrocyclone sizes, operating conditions, classification duties, and commodities was developed based on extensive circuit surveys. The database was used to evaluate the hydrocyclone performance. Among the key operational issues observed were poor circuit control strategies, improper hydrocyclone sizing and operation in the roping condition. Analysis of long-term operational data indicated that hydrocyclone feed solid density is an essential operating variable that needs to be controlled to maintain the cut size. An increase in hydrocyclone feed density leads to an increase in cut size. Almost 50% of the hydrocyclones (in the database) were operating in the roping condition. Besides the hydrocyclone feed solid density, high amounts of fine particles (−25 μm) in the hydrocyclone feed also caused the roping condition. Further research is required to operate the hydrocyclone in a spraying condition when the feed has high solid-density and a high content of fines. Plitt’s cut size model was fitted to the data set to evaluate its capability to be used in the stirred mill’s hydrocyclone. The analysis shows the Plitt’s model can predict the cut size when the hydrocyclone is in spraying mode. This result indicates that Plitt’s model can be used for the regrind duty hydrocyclones. An empirical model was developed relating the hydrocyclone feed density and the Plitt onset roping hydrocyclone underflow density. This model can be used to predict the roping condition. Finally, the impact of hydrocyclone performance on circuit performance was compared through the size specific energy of the mill. High size specific energy values were observed when the hydrocyclone is operating in the roping condition. These findings are based on the real operating condition, and it shows the importance of operating the hydrocyclone optimally to achieve overall circuit efficiency

New insights into comparison of breakage testing techniques

In order to deal with the problems of existing comminution models a new approach towards the development of mechanistic models has been made so as to better understand the physics of milling processes and environments. Despite enormous improvement in this field a comprehensive study of rock breakage characterisation, appropriate for use in these types of models, is still scarce. This paper reviews the existing models of comminution according to ore characterisation techniques and parameters. The authors have looked into the existing testing methods and their applied mechanisms of breakage, using standard test results available at the JKMRC. The study includes classifying testing devices such as the drop weight tester, rotary breakage tester, slow compression, and piston and die based on the few major fundamental mechanisms of breakage that are experienced by rocks in the breakage process. The paper compares the range of particle size and energy utilisation, applied strain rates and loading mechanisms for the equipment. The product size distributions from the various equipment is compared for equivalent input energies, various loading rates but the same level of energy intensity, a broad range of energy including low energy utilisation and fines generation rate for equivalent specific energy input. The results clearly show that the outcomes and conclusions on competence and energy for breakage are a function of the test method that is applied. In ongoing work, it is proposed to investigate common tests that can be applied to characterising ores in a manner suited to modelling a range of comminution devices