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In the process industry the use of concentrated acids is crucial to achieve desired extractions and to reduce otherwise lengthy process times. More often, acid is added in excess. Once reactions are complete, the residual acid must be gradually neutralized with base, to effect metal separations and recovery followed by a final neutralization and environmental disposal. From the cost and environmental protection points of view, it is very advantageous to have a means of monitoring solution free acidity online and in real-time. Recently in the University of Toronto's Aqueous Process Engineering and Chemistry group a technique was developed to measure the free acidity of a solution from ambient temperature up to 260°C by using eletrodeless conductivity. The sensor operates on the basis of induction currents and is suitable for very high ionic strength solutions. Acidity measurements within 5% of titrated values are possible for a wide variety of processes. Accurate online free acidity measurements have been made in high pressure acid leach (HPAL) autoclaves for both limonitic and saprolitic ores where the metals concentration varies greatly throughout the leach time. The technique has also been applied to highly concentrated electrowinning streams and oxidative acid leaching processes. Solid particles that would otherwise foul conventional cells have little to no effect on the electrodeless sensor, making it ideal for process slurries.

Conference Presentations:

Saini R.S. and Papangelakis V.G., 2008. Acid and Solution Quality Measurements via Electrodeless Conductivity. Invited speaker, Centre for Chemical Process Metallurgy annual meeting (CCPM), Toronto, ON, Canada.

Saini R.S. and Papangelakis V.G., 2008. Acid Measurements via Electrodeless Conductivity. In: 58^th Canadian Chemical Engineering Conference (CSChE 2008), Ottawa, ON, Canada.

Saini R.S., Huang M. and Papangelakis V.G., 2009. Acid Measurements via Electrodeless Conductivity. In: 92^nd Canadian Chemistry Conference and Exhibition Conference (CSC 2009), Hamilton, ON, Canada.

Saini R.S. and Papangelakis V.G., 2009. On-Line Acid Measurements via Electrodeless Conductivity in HPAL Processes for Nickel/Cobalt Extraction. In: COM2009 in Conjunction with Nickel & Cobalt (COM 2009), Sudbury, ON, Canada.

Conference Proceedings:

Saini R.S. and Papangelakis V.G., 2009. On-Line Acid Measurements via Electrodeless Conductivity in HPAL Processes for Nickel/Cobalt Extraction. In: COM2009 in Conjunction with Nickel & Cobalt, Sudbury, ON, Canada.

Pressure oxidation’s dominance in processing gold bearing refractory ores can continue to grow and maintain high capacity plants if it can treat ores with high carbonate content by providing a more effective and environmentally friendly hydrometallurgical alternative to roasting ores for gold recovery. The traditional acid pressure leach process operating at temperatures around 225°C and under oxygen overpressure, produces greenhouse emissions of CO2 and reduces the oxidative power of oxygen. Alkaline pressure oxidation prevents the formation of CO2. It is believed that sodium carbonate can also be added to the feed to prevent the formation of gypsum products within the autoclave in favor of the more soluble sodium sulphate product. The latter results in faster pyrite decomposition rates and consequently enhanced gold recoveries. In this work, the effectiveness of sodium carbonate as an additive to synthetic and clean pyrite-calcium carbonate mixtures is investigated at 200°C in a pressure reactor.

Alkaline Pressure Oxidation of Refractory Gold Ores

Sammy Peters

MASc Candidate

Evaluating the Potential of Scaling due to Calcium Compounds in Hydrometallurgical Processes

Ghazal Azimi

PhD Candidate

My PhD thesis involves developing a reliable thermodynamic model to describe and predict the chemical behaviour of different minerals in multicomponent aqueous electrolyte systems over wide ranges of temperature and pressure up to 300ºC and 80 bar, respectively. The model developed is based on the Mixed Solvent Electrolyte (MSE) model of the OLI software which provides a thermodynamic framework for successful modelling of aqueous chemistry from infinite dilution to the pure solute limit. In this work, a suitable experimental setup was also established for measuring the thermodynamic properties (such as solubility, pH and conductivity) in multicomponent aqueous solutions at high temperatures and pressures. There is no data available in the literature for such systems under these extreme conditions which shows the novelty of the experiments. These measurements will provide unique data that are helpful in validating the predictability of the model developed as well as providing a practical experimental framework for new electrolyte systems. The results of this work are applicable to several industrial fields that employ high temperature and pressure aqueous solutions such as nuclear power generation, pulp and paper, oil and gas, as well as hydrometallurgical processes.

Awards:

• Gordon Ritcey Award (2009)

• Ontario Graduate Scholarship (OGS) Award (2009–2010, 2008–2009)

• TATP Teaching Excellence Award in University of Toronto (2008)

• Helen Cross Award (2008)

• CIM MetSoc Hydrometallurgy Student Conference Award (2008)

• Tyrell Fellowship Excellence Award (2007)

• Wallberg Research Fellowship (2006)

Publications:

Azimi G., Papangelakis V.G., Dutrizac J.E. 2009. Development of a chemical model for the solubility of calcium sulphate in zinc processing solutions. Canadian Metallurgical Quarterly, in press.

Azimi G., Papangelakis V.G. 2009. Thermodynamic modeling and experimental measurement of calcium sulphate solubility in complex aqueous solutions. Fluid Phase Equilibria, in press.

Azimi G., Papangelakis V.G., Dutrizac J.E. 2008. Development of an MSE-based chemical model for the solubility of calcium sulphate in mixed chloride-sulphate solutions. Fluid Phase Equilibria, 266, No.1-2, 172‑186.

Azimi G., Papangelakis V.G., Dutrizac J.E. 2007. Modelling of calcium sulphate hydrates solubility in concentrated multi-component sulphate solutions. Fluid Phase Equilibria, 260, No. 2, 300-315.

Seyfkar N., Azimi G., Ghotbi C., Taghikhani V. 2004. Application of the non‑primitive-MSA-based models in predicting the activity and the osmotic coefficients of aqueous electrolyte solutions. Fluid Phase Equilibria, 221, 189-196.

Ghotbi C., Azimi G., Taghikhani V., Vera J. H. 2003. On the correlation of the activity coefficients in aqueous electrolyte solutions using the K-MSA model. Ind. Eng. Chem. Res. 42, 1279-1284.

Chemical Modeling of Ammonia Solutions in Ni/Co Hydrometallurgy

Sam Roshdi

PhD Candidate

Chemical modeling is becoming increasingly useful in the development, analysis, design and control of industrial chemical processes, particularly in hydrometallurgy. Chemical modeling is a very powerful tool to predict and understand the behaviour of complex aqueous systems such as ammoniacal systems containing Ni, Co, Cu, Zn sulphates, and ammonium sulphate. The vapour pressure of ammonia in aqueous ammoniacal multicomponent solutions is being studied by using the Mixed Solvent Electrolyte (MSE) thermodynamic framework implemented in the OLI software.

CURRENT PROJECTS

Recovery of Base Metals from Slags by High Pressure Oxidative Leaching

Ilya Perederiy

PhD Candidate

There are large amounts of non-ferrous slags dumped from nickel and copper smelters all over the world each year. Recovery of base metal values from this kind of slags is important not only for saving metal resources, but also for protecting the environment. The conventional method for recovery of base metals from the slags is re-smelting, which is very costly. However, no one to date has come up with an ecommimically viable process for re-treatment of the waste dump slags. In this study, a high pressure oxidative acid leaching technology was applied for the treatment of dump smelter slags. The selective leaching of valuable metals with extractions of 97.4-99.5% for Ni, Co, Cu and Zn, and about 1% for iron was achieved. The produced residue containing less that 0.03% of heavy metals can be discarded safely. A poster about this project is available for viewing in Adobe Acrobat format (pdf).

Publications:

Yunjiao Li, Ilya Perederiy, Vladimiros G. Papangelakis, “High Pressure Oxidative Acid Leaching of Nickel Smelter Slag: Characterization of Feed and Residue” Hydrometallurgy, 97 (3), 185-193, Jul 2009.

Yunjiao Li, Ilya Perederiy, Vladimiros G. Papangelakis, “Cleaning of waste smelter slags and recovery of valuable metals by pressure oxidative leaching” Journal of Hazardous Materials 152, 607–615, 2008.

Leaching of Laterite Ores with Molten Salt Hydrates

Kevin McLean

MASc Candidate

Nickel extraction from laterite ores will continue to become more important as global sulphide ore reserves dwindle.  Current hydrometallurgical processes for laterites focus mainly on pressure acid leaching with sulphuric acid.  Using molten salt hydrates (MSHs) such as MgCl₂^.6H₂O as lixiviants has not been investigated to date, but this approach has several potential advantages, such as: the ability to operate at temperatures above 100°C at 1 atm, the suppression of Mg and Fe leach, and high acid strength.  In this study, leaching experiments will be conducted in an agitated kettle varying the temperature, acid addition, and MgCl₂ concentration.

Awards:

• Ontario Graduate Scholarship (OGS) award (2009-2010)

• Best Graduate Poster at the Nickel and Cobalt 2009 Conference

Posters:

COM 2009 (Sudbury) poster

Direct (in-situ) pH Measurement at High Temperature and Pressure in Hydrometallurgical Processes

Zoran Jankovic

PhD Candidate

A special once flow-through hydrothermal cell made of Titanium grade 5 provides the required high temperature and pressure environment. A flow-through YSZ (yttria stabilized zirconia) electrode is used as the pH sensor and a flow-through Ag/AgCl electrode as the reference. The silver/silver chloride element is placed at ambient temperature to prevent any thermal degradation. Computer software will be used to convert the voltage difference to pH values.

Publications:

Z. Jankovic, V.G. Papangelakis and S.N. Lvov, “Effect of nickel sulphate and magnesium sulphate on pH of sulphuric acid solutions at elevated temperatures,” J. Appl. Electrochem., 39(6), 2009, 751.

V.G. Papangelakis, D.S. Seneviratne, Z. Jankovic, X.Y. Zhou, and S.N. Lvov, “pH measurements in High-Temperature Hydrometallurgical Systems,” Hydrometallurgy 2003 – Fifth International Conference in Honour of Professor Ian Ritchie (Eds. C.A. Young, A.M. Alfantazi, C.G. Anderson, D.B. Dreisinger, B. Harris and J. James), TMS, Warrendale PA, pp. 645-656.

S.N. Lvov, X.Y. Zhou, S.M. Ulyanov, Z. Jankovic, and V.G. Papangelakis, “In-situ pH Monitoring of High Concentration Sulfuric Acid and Acidified Geothermal Brines at Elevated Temperatures,” Pressure Hydrometallurgy 2004, (Eds.  M.J. Collins and V.G. Papangelakis), 34th Annual Hydrometallurgy Meeting of CIM, CIM, Montreal, QC, pp. 561-576, 2004.

PAST PROJECTS

Monitoring Free Acid in Hydromellurgical Solutions with an Electrodeless Conductivity Sensor

Ramanpal Saini

Graduated with an MASc degree (Oct 2009)

Recovery of Rare Earth Ions Adsorbed on Clay Minerals

Georgiana Moldoveanu

Post-Doc

Rare earths (RE) compounds are “hi-tech” materials used in electronics, automotive catalytic converters, glass/ceramics, permanent magnets, and nuclear energy. High demand/tight supply issues prompt the need for intensive research in the field of RE recovery/purification, with emphasis on development of new sources to secure sustainable access to supply in the future.

Due to of their abundance in the superficial layers in nature, high specific surface area for adsorption and relative ease of mining/processing, clay minerals containing silica and alumina (kaolinite and smectite) warrant a detailed study as important alternative sources of RE.

The adsorbed RE are leached/extracted with highly-concentrated metal salts (e.g. ammonium sulphate, ammonium chloride), and recovered/separated as high purity end-products either by solvent extraction or ion-exchange as individual elements or precipitated with excess of oxalic acid to form oxalates that are subsequently converted to RE oxides via roasting.

The present research project aims to: (a) investigate and understand the underlying mechanism of the adsorption /desorption of rare earths ions on clay materials in order to optimize the rare earth recovery step and (b) identify other possible sources of RE as well as alternative leaching procedures/reagents tailored to the specific nature of the RE-bearing mineral.

Study of Thermodynamic Properties of Aqueous Systems

Irina Bylina

Post-Doc (2005-2008)

With the help of a calorimeter, heat capacities of salts and aqueous electrolyte solutions were measured. Another focus of this study was the enthalpy changes of minerals leached at elevated temperatures and pressures using a mixing cell.

Publications:

Bylina, L. Trevani, S. C. Mojumdar, P. Tremaine and V. G. Papangelakis, “Measurement of Reaction Enthalpy During Pressure Oxidation Of Sulphide Minerals,” Journal of Thermal Analysis and Calorimetry, Vol. 96 ,2009, 1, 117–124.

Magnesium Solubility in Mixed Electrolytes

Matthew Jones

Graduated with an MASc degree (Sep 2008)

It had been found that introducing sulphates into high-strength chloride solutions will induce the precipitation of Magnesium in the form of kieserite.  Recently developed hydrometallurgical processes were attempting to utilize this behaviour in order to reject magnesium from process streams in a cost effective manner.  The purpose of this project was to use OLI Software to model this behaviour.  In order to do this, ionic interaction parameters and reference state properties were determined using existing literature data and added to the OLI Mixed Solvent Electrolyte database of thermodynamic parameters.

Publications:

M.W. Jones, V.G. Papangelakis, and J.D.T. Steyl, “Kieserite Solubility in the Aqueous FeCl₃ + MgCl₂ + HCl System between (338 and 378) K,” J. Chem. Eng. Data, 54 (7), 2009, pp 1986–1990.

Recovery of Base Metals from Slags by High Pressure Oxidative Leaching

Morteza Baghalha and Yunjiao Li

Post-Docs (1999-2001 and 2005-2007)

There are large amounts of non-ferrous slags dumped from nickel and copper smelters all over the world each year. Recovery of base metal values from this kind of slags is important not only for saving metal resources, but also for protecting the environment. The conventional method for recovery of base metals from the slags is re-smelting, which is very costly. However, no one to date has come up with an ecommimically viable process for re-treatment of the waste dump slags. In this study, a high pressure oxidative acid leaching technology was applied for the treatment of dump smelter slags. The selective leaching of valuable metals with extractions of 97.4-99.5% for Ni, Co, Cu and Zn, and about 1% for iron was achieved. The produced residue containing less that 0.03% of heavy metals can be discarded safely.

Publications:

Yunjiao Li, Ilya Perederiy, Vladimiros G. Papangelakis, “High Pressure Oxidative Acid Leaching of Nickel Smelter Slag: Characterization of Feed and Residue” Hydrometallurgy, 97 (3), 185-193, Jul 2009.

Yunjiao Li, Ilya Perederiy, Vladimiros G. Papangelakis, “Cleaning of waste smelter slags and recovery of valuable metals by pressure oxidative leaching” Journal of Hazardous Materials 152, 607–615, 2008.

M. Baghalha, V.G. Papangelakis, W. Curlook, "Factors Affecting the Leachability of Ni/Co/Cu Slags at High Temperature," Hydrometallurgy 85 (2007) 42-52.

M. Baghalha, V.G.Papangelakis, W. Curlook, Factors affecting the leachability of Ni/Co/Cu slags at high temeperature. Hydrometallurgy 85 (2006) 42-52.

W. M. Curlook, V. G. Papangelakis and M. Baghalha, “Pressure acid leaching of non-ferrous smelter slags for the recovery of their base metal values,” Pressure Hydrometallurgy 2004, (Eds.  M.J. Collins and V.G. Papangelakis), 34th Annual Hydrometallurgy Meeting of CIM, CIM, Montreal, QC, pp. 823-838, 2004.

Electrical Conductivity and Acidity of High Temperature Aqueous Sulphate Solutions

Ming Huang

Graduated with a PhD degree (April 2007)

The main goal of this work was to investigate the inter-relationship between the measured conductivities and the acidities of high temperature aqueous sulphate solutions. To undertake this research, the conductivity cell developed previously (by Dr. Morteza Baghalha) was used to measure the electrical conductivity of simulated laterite leach slurries at temperatures up to 250 °C. Acidities were measured with the new pH sensor and estimated with chemical models to enable the development of a model capable of estimating acidities of high temperature sulphate solutions based on conductivities.

Publications:

M. Huang and V.G. Papangelakis, "High Temperature Conductivity Measurements of  Concentrated NaCl-H₂SO₄-H₂O Solutions up to 250 °C", Ind. Eng. Chem. Res., 2009, 48, 2781–2785.

H. Ming and V.G. Papangelakis, "Electrical Conductivity of Concentrated Al₂(SO₄)₃-MgSO₄-H₂SO₄ Aqueous Solutions up to 250 °C", Industrial and Engineering Chemistry Research 46 (5) 1598-1604, 2007

H. Ming and V.G. Papangelakis, "Electrical Conductivity of Concentrated MgSO₄- H₂SO₄ Solutions up to 250 °C", Industrial and Engineering Chemistry Research, 45 (13); 4757-4763, 2006.

Hematite Solubility in H₂SO₄ from 130-170 ºC and 230-270 ºC

Michael Reid

Graduated with an MaSc degree (2005)

In the study, hematite solubility data was generated for 0.1-0.7 molal H₂SO₄ solutions at 130-170ºC and 230-270ºC. These measurements represent an improvement over previous experimental data due to better in-situ filtration of samples and inhibition of ferric iron reduction on titanium.

From Low Grade Iimonite to TiO₂ Using Hydrometallurgy: Kinetic Study on Leaching of Iimonite in HCl/H₂SO₄.

Gursaran Singh

Graduated with an MaSc degree (2005)

Modelling of the Nickel and Cobalt Kinetics During Pressure Acid Leaching of Laterites Using Aspen Plus 11.1 and OLI.

Miranda Cheung

Graduated with an MaSc degree (2004)

Gypsum Scale Abatement in Continuous Hydrometallurgical Reactors

Jeffrey Adams

Graduated with a PhD degree (2004)

The objective of the work was to determine the rate of gypsum scale formation in continuous stirred reactors. Effect of pH, temperature, residence time were studied experimentally in order to elucidate the mechanism of scale growth, and eventually to reduce the scale in industrial reactors.

Publications:

J. F. Adams, and V.G. Papangelakis, "Optimum Reactor Configuration for Prevention of Gypsum Scaling During Continuous Sulphuric Acid Neutralization," Hydrometallurgy 89 (2007) 269-278.

J.F. Adams and V.G Papangalakis, "Gypsum Fouling in Neutralization Reactors and Aqueous Streams", Hydrometallurgy 2003, Proceedings of the 5th International Symposium Honoring Professor Ian M. Ritchie v.2, (eds. C. Young, A. Alfantazi, C. Anderson, A. James, D. Dreisinger and B. Harris), TMS, Warrendale, PA 1741 - 1753, 2003.

J.F. Adams and V.G. Papangelakis, "Understanding Gypsum Crystallization Fouling in Sulphuric Acid Neutralization Reactors", Gypsum and Fly Ash 2002, Process Ortech Inc., Toronto, Canada, 4-1 - 4-15, 2002.

J.F. Adams and V.G. Papangelakis, "Gypsum Scale Formation in Continuous Neutralization Reactors", Canadian Metallurgical Quarterly, 39 (4), 421-432, 2000.

Development of Novel Experimental Techniques for Pressure Oxidation of Nickel Sulphide Ore

James Brown (2004)

Graduated with an MASc degree

A custom-made titanium autoclave (high-pressure reaction vessel) having three quartz windows was equipped with a high-speed imaging system to monitor and quantify the production of elemental sulphur in real time under various reaction conditions. The wetting and adhesion force of liquid sulphur on the mineral surface was determined by measuring the surface tension and contact angle.

Publications:

J. A. Brown and V.G. Papangelakis, “Interfacial studies of liquid sulphur during aqueous pressure oxidation of nickel sulphide,” Minerals Engineering, 18, 1378 - 1385, 2005.

High Temperature Thermodynamic Modelling of Autoclave Laterite Leaching Systems

Jesus Casas and Haixia Liu

Visiting Professor and Research Associate

Publications:

H. Liu and V.G. Papangelakis, “Solubility of Pb(II) and Ni(II) in mixed sulphate-chloride solutions with the Mixed Solvent Electrolyte model,” Industrial and Engineering Chemistry Research, 45(1), 39 – 47, 2006

J. M. Casas, V.G. Papangelakis and H. Liu, “Comparison of Three Activity Coefficient Models on the High Temperature Aqueous Al₂(SO₄)₃-MgSO₄-H₂SO₄-H₂O System,” Industrial and Engineering Chemistry Research, vol 44(9), 2931-2941, 2005.

H. Liu and V.G. Papangelakis, “Thermodynamic equilibrium of the O₂ – ZnSO₄ – H₂SO₄ – H₂O System from 25 to 250?C,” Fluid Phase Equilibria, 234, 122-130, 2005.

H. Liu and V.G. Papangelakis, “Chemical Modelling of High Temperature Aqueous Processes”, Hydrometallurgy, 79, 48-61, 2005. 

H. Liu, V.G. Papangelakis, M.S. Alam, and G. Singh, "Solubility of Hematite in H2SO4 Solution at 230-270°C", Canadian Metallurgical Quarterly , 42(2), 199 - 208, 2003.

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