Fernando O. Durão

Control of a flotation column using fuzzy logic inference

This paper describes a fuzzy controller that was developed for the control, in real time, of three main variables of the column flotation process. Column flotation is a solid-solid separation process based on the physical and chemical properties of mineral particle surfaces. It is applied to the concentration of low grade ores and to ores that require very fine grinding to achieve mineral liberation. The economic exploitation of the process, guaranteeing the desired final product characteristics from a feed of varying composition, requires a stable operation, which is accomplished through the automatic control of some key process variables. The difficulties encountered in the development of process controllers for this process are related to the lack of reliable measuring devices for the process variables involved, with the non-existence of mathematical dynamical models that can be used in a controller synthesis and with its non-linear and time-varying behaviour. The process and the problems related with its control are briefly explained and the main reasons for fuzzy logic control application are discussed. The real time control system and the fuzzy controller structure and parameters are presented. A general overview of the pilot plant where the experimental work was performed is presented. Finally, results of the experimental work, carried out with the two-phase system (air and water), are summarised and the conclusions are drawn.

Separation of packaging plastics by froth flotation in a continuous pilot plant

The objective of the research was to apply froth flotation to separate post-consumer PET (Polyethylene Terephthalate) from other packaging plastics with similar density, in a continuously operated pilot plant. A representative sample composed of 85% PET, 2.5% PVC (Polyvinyl Chloride) and 11.9% PS (Polystyrene) was subjected to a combination of alkaline treatment and surfactant adsorption followed by froth flotation. A mineral processing pilot plant, owned by a Portuguese mining company, was adapted for this purpose. The experimentation showed that it is possible to produce an almost pure concentrate of PET, containing 83% of the PET in feed, in a single bank of mechanical flotation cells. The concentrate grade attained was 97.2% PET, 1.1% PVC and 1.1% PS. By simulation it was shown that the Portuguese recycling industry specifications can be attained if one cleaning and one scavenger stages are added to the circuit.

Hydrometallurgical recycling of lithium-ion batteries by reductive leaching with sodium metabisulphite

The hydrometallurgical extraction of metals from spent lithium-ion batteries (LIBs) was investigated. LIBs were first dismantled and a fraction rich in the active material was obtained by physical separation, containing 95% of the initial electrode, 2% of the initial steel and 22% of plastic materials. Several reducers were tested to improve metals dissolution in the leaching step using sulphuric acid. Sodium metabisulphite led to the best results and was studied in more detail. The best concentration of Na2S2O5 was 0.1 M. The metals dissolution increased with acid concentration, however, concentrations higher than 1.25 M are unnecessary. Best results were reached using a stirring speed of 400 min-1. The metals leaching efficiency from the active material (Li, Mn, Ni, Co) increased with the temperature and was above 80% for temperatures higher than 60 °C. The dissolution of metals also rose with the increase in the liquid/solid ratio (L/S), however, extractions above 85% can be reached at L/S as lower as 4.5 L/kg, which is favourable for further purification and recovery operations. About 90% of metals extraction can be achieved after only 0.5 h of leaching. Sodium metabisulphite can be an alternative reducer to increase the leaching of Li, Mn, Co, and Ni from spent LIBs.

Kinetic approach to the study of froth flotation applied to a lepidolite ore

The number of published studies related to the optimization of lithium extraction from low-grade ores has increased as the demand for lithium has grown. However, no study related to the kinetics of the concentration stage of lithium-containing minerals by froth flotation has yet been reported. To establish a factorial design of batch flotation experiments, we conducted a set of kinetic tests to determine the most selective alternative collector, define a range of pulp pH values, and estimate a near-optimum flotation time. Both collectors (Aeromine 3000C and Armeen 12D) provided the required flotation selectivity, although this selectivity was lost in the case of pulp pH values outside the range between 2 and 4. Cumulative mineral recovery curves were used to adjust a classical kinetic model that was modified with a non-negative parameter representing a delay time. The computation of the near-optimum flotation time as the maximizer of a separation efficiency (SE) function must be performed with caution. We instead propose to define the near-optimum flotation time as the time interval required to achieve 95%–99% of the maximum value of the SE function.

Optimization of Lithium Extraction from Lepidolite by Roasting Using Sodium and Calcium Sulfates

ABSTRACT The lithium extraction from a lepidolite concentrate using roasting, followed by water leaching, was studied. Several alternative additives were initially tested. The use of sodium and calcium sulfates as additives was evaluated in more detail. The influence of some process variables, namely the roasting time, roasting temperature and the additive/concentrate mass ratio, was studied applying a design of experiments. The lithium extraction was modelled and the fitted and validated model was used to optimize the process response. The increase in the additive/concentrate mass ratio, roasting time and temperature seems to result in solid state reactions and transformations that lead to phase, morphological and particle size distribution modifications, which were assessed by XRPD, SEM, and particle size analyses. In this process, lithium sodium sulfate formation constitutes a crucial step enabling the Li water leaching. High lithium extractions were estimated for several combinations of factors. At 850°C, lithium extractions over 90% are obtained when the roasting time is above 1.90 hour and the additive/concentrate mass ratios are over 0.77. An increase in the temperature to 875°C also leads to lithium extractions over 90% for a roasting time of 1 hour and an additive/concentrate mass ratio of 0.60.

Supervisor fuzzy controller of a flotation column

Abstract This paper describes a supervisor fuzzy controller of a pilot flotation column. The flotation column processes a clay composed mainly of kaolinite and quartz, reducing the iron grade of the final product to be used in the preparation of ceramic pastes. The main control objective (top level control) is to keep the iron content in the underflow stream close to target specification. At the intermediate level, three process variables are controlled by fuzzy logic inference: collection zone height, air holdup in the collection zone and bias water flow rate. The lower level of control manipulates the process stream flow rates by means of PID controllers.

Optimization of an innovative approach involving mechanical activation and acid digestion for the extraction of lithium from lepidolite

The recovery of lithium from hard rock minerals has received increased attention given the high demand for this element. Therefore, this study optimized an innovative process, which does not require a high-temperature calcination step, for lithium extraction from lepidolite. Mechanical activation and acid digestion were suggested as crucial process parameters, and experimental design and response-surface methodology were applied to model and optimize the proposed lithium extraction process. The promoting effect of amorphization and the formation of lithium sulfate hydrate on lithium extraction yield were assessed. Several factor combinations led to extraction yields that exceeded 90%, indicating that the proposed process is an effective approach for lithium recovery.

Testing some Connectionist Approaches for Thematic Mapping of Rural Areas

An overview of several supervised classification methodologies applied at the research centre CVRM to automatic classification of remote sensing data is presented. Some classification methodologies based on Artificial Neural Networks are roughly described, with emphasis on Multilayer Feed-forward Networks (MLFN) trained with the Back-propagation algorithm and on Probabilistic Neural Networks (PNN). A technique under study at the CVRM for reducing training time, conjugating Principal Components Analysis and Genetic Algorithms, is outlined. Finally a case study is presented, describing an application of a MLFN and a PNN to a pixel based multispectral (6 bands) Landsat TM data from the rural Moura-Ficalho area (South of Portugal). The results were mapped and the performances compared, by means of confusion matrices and also by the computing time used, with a typical parametric approach such as the classical Maximum Likelihood Classifier and with field work interpretation.

Optimization of metals extraction from spent lithium-ion batteries by sulphuric acid and sodium metabisulphite through a techno-economic evaluation

The main factors that affect the extraction of metals from spent lithium-ion batteries by acid leaching using H2SO4, and sodium metabisulphite, were evaluated and optimized through a set of experiments, framed by a techno-economic approach. The maximum value of the profit response was obtained with the highest possible values of acid concentration (2.5 M) and time (2 h), a liquid/solid ratio of 5 L/kg, and the lowest possible value of temperature (40 °C). After leaching, the electrodes active material contained in the metals decreased, while it was still significant in the graphite, as observed by scanning electron microscopy-energy dispersive spectrometry and x-ray powder diffraction. Even though the performed economic evaluation was a summarized outline it can be considered suitable to compare different leaching conditions and to determine the possible best combinations of factors that can optimize the profit response.