Alison Lewis

• University of Cape Town

Rare earth elements (REEs) are essential for permanent magnets that are vital for wind turbines and electric vehicles motors (EV), and are also used in a range of high-tech devices such as smartphones, digital cameras, and electronic displays. Nickel metal hydride (NiMH) batteries have been identified as a potential source due to their short lifesp...

South Africa produces significant quantities of brines but there is insufficient information on their biological and physicochemical characteristics and nature, which limits the ability to propose sustainable brine handling procedures. This study aimed to comprehensively characterize selected brines from major brine-producing industries in South Af...

Antisolvent crystallization is a separation technology that separates the solute from the solvent by the addition of another solvent, in which the solute is sparingly soluble. High yields are achieved by using higher antisolvent-to-aqueous ratios, but this generates higher supersaturation, which causes excessive nucleation. This results in the prod...

Eutectic Freeze Crystallization (EFC) is a separation technology that separates solute from solvent by cooling the brine to a temperature below its eutectic point, such that ice and salt simultaneously crystallize out of the solution. Achieving consistent production of ice and salt at high production rates has been a challenge for EFC. This is due...

Eutectic freeze crystallization (EFC) is a novel separation technique that can be applied to treat brine solutions such as reverse osmosis retentates. These are often a mixture of different inorganic solutes. The treatment of calcium sulphate-rich brines using EFC often results in gypsum crystallization before any other species. This results in gyp...

Ice scale formation is one of the main impediments to the successful implementation of eutectic freeze crystallization (EFC). Controlling the formation of ice scale on heat exchanger (HX) surfaces has been attempted by using mechanical scrapers, with limited success in EFC. Some of these limitations have been associated with the HX surface properti...

Interest in the recoveryRecoveryof Rare EarthRare earthsElementsRare earth elements (REEs) has increased significantly in the last few years. There has been a concomitant increase in research and in process developmentProcess development for REE recoveryRecovery [1]. Antisolvent crystallizationCrystallization has the potential to recover REE from s...

Mining activities generate Acid Mine Drainage (AMD) and wastewater streams rich in dissolved inorganic species that negatively affect water quality. Conventional lime treatment of AMD leads to the precipitation of a voluminous sludge, comprising mainly of Ferri-Oxyhydroxide (Fe-O-OH) and gypsum, whose matrix renders it difficult to dewater. Such pr...

As salt and ice are crystallized from multi-component saline solutions, the concentrations of the non-crystallizing salt species increase until the system is saturated with more than two species. This study showed that, in such a situation, seeding can be employed to control the crystallization kinetics of the salts. The aim of this study was to de...

Previous research in South Africa has identified gaps in wastewater quality characterisation and remediation. Wastewater quality indicators need to be known in order to reuse, recycle, and/or recover resources, but are poorly reported for wastewater streams. Formal and relational approaches were used to access wastewater quality information. Relati...

Previous research in South Africa has identified gaps in wastewater quality characterisation and remediation. Wastewater quality indicators need to be known in order to reuse, recycle, and/or recover resources, but are poorly reported for wastewater streams. Formal and relational approaches were used to access wastewater quality information. Relati...

Continuous crystallization is an area of intense research, with particular respect to the pharmaceutical industry and fine chemicals. Improvements in continuous crystallization technologies offer chemical industries significant financial gains, through reduced expenditure and operational costs, and consistent product quality. Written by well-known...

In the continuous lime neutralization treatment of iron-laden wastewaters, such as acid mine drainage (AMD), the solid-liquid separation of iron solids formed is difficult to effect. The particle formation mechanisms, the ensuing particle size and size distribution – which in turn shape the dewatering process – are strongly influenced by the OH/Fe...

Eutectic Freeze Crystallization (EFC) is a potentially cost-effective method to treat reverse osmosis (RO) brines, through the simultaneous crystallization of ice and salt. A major operational challenge, limiting the implementation of EFC in industry, is the formation of an ice scale layer on heat exchanger surfaces. This research determined the in...

After the kraft or soda pulping of lignocellulosic materials to produce pulp suitable for papermaking, the spent pulping liquor typically has been recovered by multi-effect evaporation, followed by incineration in a recovery boiler. This review article considers one unit operation, eutectic freeze crystallization (EFC), that may have potential to s...

In this chapter, we discuss classical and nonclassical concepts of crystal growth that coexist in the literature as explanations for the formation of both mono- and polycrystalline particles, often of the same substances. Crystalline particles with intraparticle nanosized subunits, nanoparticulate surface features, and complex morphologies have led...

This study aimed to investigate factors that affect the conversion of sulphates and magnesium, and the recovery of gypsum and magnesium hydroxide in the neutralization of a sulphate rich stream using calcium hydroxide, in a laboratory scale seeded fluidised bed crystallizer. Particular focus was on reducing the precipitated fines that escaped with...

The presence of impurities in solution during crystallization can influence the crystallization kinetics of the desired product. Consequently, this affects the product quality parameters such as the crystal size distribution (CSD), purity and morphology. This paper focuses on the application of eutectic freeze crystallization (EFC) to the purificat...

Precipitation is the process of solid formation from solution by means of a reaction. It is most frequently used in the removal and recovery of metals from solution. In scientific terms, precipitation is affected by a chemical reaction that forms a salt whose solubility in solution is exceeded. The thermodynamic driving force causing precipitation...

In order to achieve high efficiency perovskite solar cells, understanding both the crystal structure and the opto-electronic properties of perovskite layers are of importance. This paper uses crystallization analysis and modelling study of two different perovskites deposition methods (two-step and one-step methods) and thereby shows that the one-st...

This book presents an assortment of case-studies pertaining to the use of sustainable technologies for heavy metal removal and recovery from mining and metallurgical wastes, construction and demolition wastes, spent catalysts and electronic wastes. Wastewaters from diverse industrial and mining activities have caused pollution problems, but these...

This book covers the principles, underlying mechanisms, thermodynamic functions, kinetics and modeling aspects of sustainable technologies, particularly from the standpoint of applying physical, chemical and biological processes for the treatment of wastewater polluted with heavy metals. Particular emphasis has been given to technologies that are b...

Eutectic freeze crystallization (EFC) has been pronounced a promising separation technique to recover ice and salt simultaneously in an energy efficient manner. Alike other freeze concentration methods, accumulation of ice layer which is commonly known as ice scaling on the heat exchanger surface during operation thwarts commercial application of E...

Reverse osmosis (RO) plants are widely used for recovering potable water from industrial wastewater streams. The RO retentate stream is highly concentrated in salts, thereby limiting further treatment using RO due to increased scaling potential of the salts. Currently, the brine streams are disposed of in evaporation ponds in which pure salts canno...

Gravitational sedimentation of suspensions in various precipitation processes is hindered by colloidal stability. This is due to the high surface charge of the suspension and results in strong attraction/interaction between the ions on the particle surface and counter-ions in solution. Moreover, this strong interaction results in a charge build-up...

The precipitation of barium sulphate in a rapid mixing device (Y-mixer) coupled with an instantaneous sample freezing device was studied in order to accurately measure the nucleation rate. In this Shock-Freeze Cryo-TEM (SFCT) approach, a small volume of solution was removed from the stream directly into liquid ethane by means of a gravitational gui...

Bridging the gap between theory and practice, this text provides the reader with a comprehensive overview of industrial crystallization. Newcomers will learn all of the most important topics in industrial crystallization, from key concepts and basic theory to industrial practices. Topics covered include the characterization of a crystalline product...

The efficacy of eutectic freeze crystallization (EFC) in crystallizers and in subsequent downstream washing or filtration steps is a direct function of size and morphology of the crystalline products. These product characteristics are influenced by supersaturation and residence time. To investigate the effect of residence time and supercooling on i...

Combined rainbow Schlieren deflectometry (RSD) and liquid crystal thermography (LCT) served as in situ non-intrusive techniques to determine local concentration and temperature fields based on refractive index gradients in solution during crystallization of sodium sulfate from aqueous solution. The combination of RSD with LCT allowed the decoupling...

A water treatment process needs to recover both water and other useful products if the process is to be viewed as being financially and environmentally sustainable. Eutectic Freeze Crystallization (EFC) is one such sustainable water treatment process that is able to produce both pure ice (water) and pure salt(s) by operating at a specific temperatu...

Interactions between heat and mass diffusion determine growth mechanisms during ice crystallization. The effects of heat and mass transfer on ice growth in pure water and magnesium sulfate solution were investigated by studying the evolution of the gradient of the refractive index using color Schlieren deflectometry. For pure water, the gradient of...

The crystallisation of ice from a 1 wt% sodium sulphate solution was investigated at different cooling rates and solution volumes in order to determine the metastable zone (MSZ) for the system. The results from this study showed that there was a large variation in nucleation temperatures, thus confirming the stochastic nature of nucleation. The res...

Surface properties of metal sulphides have a great significance in various areas of engineering and science, such as acid mine drainage, contaminant sorption, and metal separation. In various attempts at producing metal sulphide particles from synthetic solutions, prodigious quantities of nuclei that grow only to colloidal dimensions have been freq...

Eutectic freeze crystallization (EFC) is a novel technique for the recovery of pure salt and pure water from hypersaline waste brines. It is therefore a promising technology for the treatment of industrial waste waters. The impurities caused by crystallizing salt out of multi-component brines by EFC have not yet been investigated, however. To these...

A novel low temperature crystallization process called eutectic freeze crystallization (EFC) can produce both salt(s) and ice from a reverse osmosis (RO) stream by operating at the eutectic temperature of a solution. The EFC reject stream, which is de-supersaturated with respect to the scaling component, can subsequently be recycled back to the RO...

The crystallisation of ice from a 1. wt% sodium sulphate solution was investigated at different cooling rates and solution volumes in order to determine the metastable zone (MSZ) for the system. The results from this study showed that there was a large variation in nucleation temperatures, thus confirming the stochastic nature of nucleation. The re...

Metal sulphide precipitation is important in several hydrometallurgical processes. However, challenges exist in solid–liquid separation and recovery of the colloidal precipitates produced in some systems. This study presents the effect of downstream processing options on the surface properties of colloidal particles produced during copper and zinc...

Metal sulphide precipitation forms an important component of acid mine drainage remediation systems based on bacterial sulphate reduction. However, the precipitation reaction is inherently driven by very high levels of supersaturation with the generation of small particles with poor solid-liquid separation characteristics. In this study, the effect...

The minerals industry is committed to the principles of sustainability. Reducing water consumption is a priority area, especially for regions of water scarcity. This paper presents a systemic optimization of the water balance of the Skorpion Zinc refinery with the aim of reducing water consumption. An Aspen Plus simulation of the process is used. T...

The nucleation rate for the precipitation of copper selenide, which has an extremely low solubility, was measured. The measured values of the kinetic parameter A and the thermodynamic constant B were compared with those calculated from theoretical considerations based on the classical nucleation theory. These calculated values were found to be phys...

The generation of hypersaline brines emanating from industrial and mining operations poses a major environmental problem globally as the volumes of these brines increase at an exponential rate. The potential risks to the surrounding environment and water resources increase proportionally with the increased generation of these brines. The need to tr...

Metal sulfide precipitation forms an important component of acid mine drainage remediation systems based on bacterial sulfate reduction. The precipitation reaction is thermodynamically favorable, but a number of technical issues remain. In this study the effect of metal to sulfide molar ratio and operating pH on the nature and settling characterist...

The removal of selenium from copper sulphate solution prior to the electrowinning of copper is desirable in order to minimise contamination of the copper cathodes by selenium and other impurities. The selenium removal is effected by a precipitation process that takes place under high supersaturation conditions, which favour nucleation over any othe...

In a sugar refinery, the juice is concentrated through evaporation, with the objective of concentrating the juice to syrup as rapidly as possible. Because the heat of vaporization of water is relatively high, the evaporation process can be highly energy intensive, and therefore the economical use of steam is important in the refinery. This paper re...

Complex, hypersaline brines originating from the mining and extractive metallurgical industries have the potential to be treated using Eutectic Freeze Crystallization (EFC). Although EFC has been shown to be effective in separating a single salt and water, it has yet to be applied to the complex hypersaline brines that are typical of reverse osmosi...

The increasing amount of waste water and effluent from South Africa's mining industry forms a growing problem, which processing requires sustainable solutions in which both the water and the dissolved component can be re-used. Eutectic freeze crystallisation (EFC) has been identified as a key technology that is not only energy efficient, but also p...

The discrimination between crystal growth and aggregation is of crucial importance for the control of morphology and particle size in crystallization processes, as they are influenced in very different ways by the industrial processing environment. A collection of resembling solution-grown polycrystalline particles that differ widely in chemical na...

Although there have been numerous studies on metal sulphide precipitation, the research field as a whole is not well integrated. This paper reviews the disparate areas of study into metal sulphide precipitation in an attempt to summarise the current work, as well as to suggest potential for future consolidation in the field. The review encompasses...

The active particulate processes in the precipitation of nickel powder by hydrogen reduction were investigated on an industrial scale by analyzing the evolution of the particle size distribution (PSD) and its derived moments. Based on this information, an appropriate model based on the moment form of the population balance equation (PBE) was tested...

The use of novel biological processes, based on the activity of SRB, has been introduced as viable alternatives for AMD treatment. However, a number of challenges exist, particularly with respect to the metal sulphide precipitation step of these processes. Metal sulphide precipitation processes are inherently driven by high degrees of supersaturati...

The active particulate processes in the precipitation of nickel powder by hydrogen reduction were investigated on an industrial scale by analyzing the evolution of the particle size distribution (PSD) and its derived moments. Based on this information, an appropriate model based on the moment form of the population balance equation (PBE) was tested...

The use of different types of seeding material to cause the layer deposition of desired iron phases is an attractive technique for the treatment of industrial waste waters, synthesis of iron products and the study of adsorption and dissolution reactions involving iron oxides. In this study, artificial solids (consisting of mainly ferrihydrite and l...

The active mechanisms in the precipitation of nickel powder by hydrogen reduction were investigated by means of mathematical models based on the moment form of the population balance equation (PBE). The objective of the work was to establish the mechanisms involved in powder formation and how these are affected by the presence of impurities. The ef...

This study is an investigation into the mechanism and kinetics of Rh3+ co-precipitation with CuS upon the addition of a large excess of aqueous thiosulfate to acidic base metal sulfate solutions, where [Rh3+] is two orders of magnitude lower than [Cu2+], over 50–150 °C. The heterogeneous cationic substitution reaction has been identified as a new p...

Eutectic freeze crystallisation technology has shown great potential for the further treatment of industrial hypersaline brines. It requires less energy than a typical 3-staged evaporative crystallizer and successfully produces pure crystalline products. The process exploits the density differences of the three phases (ice, salt and mother liquor)...

Eutectic Freeze Crystallization (EFC) offers a novel method of treating brines and concentrates in order to recover pure water and salt. Because the heat of fusion of ice (6.01 kJ/mol) is six times less than the heat of evaporation of water (40.65 kJ/mol), the energy required to separate the water as ice is significantly less than that required to...

The oxidation and subsequent precipitation of iron from solutions are very important for most hydrometallurgical wastewater treatment practitioners. The particle formation process mechanisms are important for shaping the dewaterability and particle size distribution of the precipitates. In this study the objective is to elucidate the mechanisms of...

In the precipitation of metal sulfides from solution, either aqueous or gaseous sources of sulfide can be used. In this work, batch aqueous and gaseous sulfide experiments confirmed that no precipitation of Ni2+ was possible when only the H2S(aq) sulfide species was available for reaction. Gaseous sulfide precipitation of Ni2+ using H2S(g) was carr...

The oxidation and precipitation of iron from ferrous sulfate solutions was studied at high Fe2+ concentrations, as found in typical South African acid mine drainage, and at high pH, as practised in the removal of iron from acid mine drainage (AMD) by the high-density sludge process. The results obtained showed that the nature of the precipitates fo...

The effect of iron on the precipitation behaviour of nickel powder was investigated. Reduction experiments were conducted on a 0.5L laboratory autoclave fitted with a Teflon reaction beaker and a double impeller configuration consisting of an upper axial impeller and lower Rushton turbine. Reduction was conducted in the presence of a morphology mod...

The generation and control of manganese sulphide particle size distribution using various mixing configurations were investigated. Specifically, this paper discusses how varying mixing intensities on a macro and micro scale affect the resultant manganese sulphide particle size distribution (PSD) at a constant concentration. The mixing variations we...

The effect of a morphology modifier on the precipitation process of nickel powder was investigated in order to develop an understanding of its mechanism of action. Experiments were conducted on a pilot-plant scale using a 75-L autoclave with modifier dosages in the range of 0.25–5vol%. Samples were collected from each successive batch reduction wit...

Solids suspension in stirred tanks is important, especially in the mineral processing industry, and it is one of the factors that influence the process economics. Computational fluid dynamics (CFD), laser Doppler velocimetry (LDV) and optical attenuation methods are employed to investigate the off-bottom solids suspension in a fully baffled tank wi...

The reaction kinetics of precipitation from aqueous solution is not only a function of the concentration of reagents but also depends on the properties of the solid particles formed in the process. These property changes arise from the increasing influence of surface properties in comparison to volumetric bulk-properties as the particle size decrea...

This study describes experiments carried out in a fluidized bed reactor (FBR) to observe the active mechanisms occurring during the precipitation of nickel hydroxy-carbonate. The fluidized bed process presented in this paper is suitable for recovery of metal ions from solutions in the form of solid coated onto a silica sand surface. The solution co...

In hydrometallurgical processes, the use of metal sulphide instead of hydroxide precipitation has gained prominence in recent decades. The arguments for its preferential use are based on the high degree of metal removal at relatively low pH values; the sparingly soluble nature of sulphide precipitates; favourable dewatering characteristics and the...

Nickel solids concentration distribution in a stirred tank was investigated using computational fluid dynamics (CFD) and experimental methods. The laser Doppler velocimetry (LDV) method was used to measure the velocity field for the liquid-only system and an optical technique was employed to determine the axial solids concentration distribution. Th...

Sulfide precipitation of nickel and cobalt was investigated in three reactors: batch, seeded fluidized bed with an aqueous sulfide source, and bubble column with a gaseous sulfide source. In terms of metal removal and settling rate, the sulfide system is more efficient than either hydroxide or carbonate. In the batch system, the kinetics of the nic...

This paper examines the active mechanisms responsible for the size enlargement of nickel metal particles during reduction by hydrogen gas. The population balance, related to particle size distribution, is discretized and solved with the method of moments to model the experimental data. This data was generated in a solution of intermittently constan...

An overview of three studies on seeded precipitation in a fluidised bed reactor (FBR) is presented. The objective of using the FBR is to remove dissolved metals as precipitated metal salts onto a seed surface. For the nickel hydroxy-carbonate system (S =±10⁵), particle enlargement was found to occur by a combination of growth and aggregation. The c...

A model framework is described for crystallization of a single solid species in a well-mixed compartment at steady state. The model framework applies to both Type I (that is, nonhigh yield) crystallization and Type II (high yield) crystallization. The framework consists of population balances incorporating nucleation, growth, aggregation, breakage,...

The capabilities of four commercial simulators to model precipitation processes is discussed via two case studies: copper(II) sulfide and cobalt(II) carbonate precipitation, respectively. Two approaches were adopted in the modeling, using various existing modeling tools or developing simulation models from an independent critical review of the lite...

The feasibility of the removal of a single metal (copper) by sulphide precipitation from a synthetic stream was investigated in a seeded fluidised bed reactor. The use of sulphide was motivated by high sulphate levels in local acid mine drainage and the potential integration of the metal removal process with a biological sulphate reducing process t...

A thermodynamic electrolyte model has been used to investigate the system MgSO4 + H2O at temperatures close to the eutectic from (0 to −10) °C. The model was based on the Pitzer aqueous electrolyte activity coefficient model using the interaction parameters proposed by Marion and Farren (Marion, G.; Farren, R. E. Mineral solubilities in the Na-K-Mg...

A thermodynamic electrolyte model has been used to investigate the system MgSO4 + H2O at temperatures close to the eutectic from (0 to -10) degrees C. The model was based on the Pitzer aqueous electrolyte activity coefficient model using the interaction parameters proposed by Marion and Farren (Marion, G.; Farren, R. E. Mineral solubilities in the...

Metallic nickel and other metals are industrially produced by the reduction of nickel diamine sulphate by hydrogen under pressure at elevated temperatures in mechanically agitated autoclaves. The nickel produced in each batch is used as a seeding agent for the reduction of the next batch of solution. With repeated batch reductions, the metallic nic...

The focus of this work is the control of the desupersaturation reactor in the Slurry Precipitation and Recycle Reverse Osmosis (SPARRO) process for desalinating water with a high calcium content. Three topics are covered in this paper: quantifying and controlling gypsum morphology, identifying and quantifying the crystallization phenomena in the re...

Overflow from an anaerobic, sulphate reducing, reactor was used to precipitate copper, iron and zinc from aqueous solutions. Two predictive methods, one generated empirically using data from synthetic solutions and one based on thermodynamic speciation software were evaluated. Both methods could accurately predict zinc precipitation. The inability...

Hydrodynamics, temperature, pH and various other physico-chemical factors influence the morphology of nickel produced via hydrogen reduction. The focus of the current work is the effect on hydrodynamics of changing the impeller and reactor configurations in a 75 l stirred vessel with draft tube and baffles. The aim was to determine which configurat...

The morphology of nickel crystals can be quantified using measurements of fractal structure. In the study described in this article, fractal dimensions of cross sections of 16 nickel samples were determined, and the numerical analysis indicates that the more rugged surfaces are characterized by higher fractal dimensions although the relationship be...

Hydroxycarbonate precipitation of nickel in a pellet reactor was investigated in a previous study (Guillard, D.; Lewis, A. E. Ind. Eng. Chem. Res. 2001, 40 (23), 5564−5569)1 in order to gain an understanding of the precipitation processes occurring inside the reactor. This paper presents the results of an attempt to establish conditions for optimum...

Secondary lead refining produces a sulphidic slag that also contains varying quantities of lead. Initially, the objectives of this project were to treat the slag in order to recover the valuable lead as well as to render the slag environmentally benign. However, in keeping with the principles of clean technology and, specifically, the approach of c...

As an aid to the design and operation of anaerobic digesters treating high sulphate waste waters, a mathematical model describing this treatment process has been developed. Apart from sulphate reduction, the model includes those reactions which occur either prior to sulphate reduction or in competition with it. These include, hydrolysis of solid su...

Particle morphology is a term that is used to describe the overall external shape and appearance of particulate solids. From the physical point of view, a precipitated solid is characterized primarily by the size and morphology of the particles (Sohnel and Garside, 1992). If the morphology of the crystal structures is to be related to the processin...

Carbonate precipitation of nickel in pellet reactors has several advantages over the more commonly used hydroxide sludge process. As a seeded precipitation, no sludge is formed; instead, there is a dense precipitate permitting easy solid−liquid separation and reuse of the nickel by dissolving the pellets. Furthermore, carbonate precipitation occurs...

The precipitation of platinum is often enhanced by the addition of wood flour; a very fine, nonvaluable material as seed. The wood flour acts as surface area for precipitate deposition that ensures the formation of reasonable sized particles and prevents undesirable mirroring and scalingon the reactor walls. However, the downstream removal of wood...

In this paper the metacognitive development of students in a second year chemical engineering course (which had such development as an explicit aim) is investigated. Journal data from the class were analysed and a framework comprising four different areas of metacognitive development was arrived at. Within each area, key shifts in approach were ide...