Professor Chris Aldrich

RESEARCH INTERESTS IN PROCESS SYSTEMS ENGINEERING

Process systems engineering is the multidisciplinary field concerned with modelling and simulation, design and synthesis, and control and optimization of chemical process systems. My research specific interests in this area are related to smart sensors, process monitoring and fault diagnosis, continuous process improvement and systems that learn from data, as outlined below.

Smart sensors and soft sensors

In many metallurgical process environments, direct measurement of process variables is problematic, owing to the aggressive environments, such as in high temperature furnaces or comminution systems. In other processes, systems states can be inferred from complex patterns of data. Research includes the interpretation of acoustic signals in plasma arc furnaces and milling systems, predicting the states of hydrocyclones by videographic monitoring of their underflow spray profiles, image-based monitoring of froth flotation cells, online monitoring of particulate feeds on conveyor belts, interpretation of electrochemical noise in aqueous corrosion systems, etc.

Process monitoring and fault diagnosis

The use of algorithms to detect and identify process faults is critically important in the efficient and safe operation of many process systems. Data-driven approaches form the mainstay of most of the methods designed to deal with complex systems. Machine learning in particular is designed to deal with large, nonlinear systems.

Learning from data

Process models form the basis of the many forms of advanced control required to deal with the challenges arising from increasingly complex operating environments. With the trend towards highly automated, large-scale, integrated process circuits, fundamental models that rely on explicit process knowledge are rarely available and therefore plant automation, process development and continuous process improvement rely increasingly on the interpretation of prodigious volumes of plant data generated by modern instrumentation. The analytical methods to achieve this comprise data mining, pattern recognition, machine learning and data visualization. Their development and application in industry is therefore a core component of my research. Examples include the development of animated data visualization for furnaces, mapping of the states of SAG mills from operational data and inference of process states from statistical process models, continuous process improvement.

Speciality Areas

CONSULTATION WORK

Consulting practice over last 30 years has been concerned mostly with the development and application of fault diagnostic methods, algorithms and software, development and international commercialization of machine vision systems for froth flotation plants and particle systems, training of company staff in statistics and quality programmes, continuous process improvement, monitoring and control of furnaces, modelling and simulation of hydrometallurgical operations, treatment of mine effluent, water purification, as well as feasibility studies and support in the applicability of plant automation in the mineral processing industries. 

2020

• Giglia, K. C., and C. Aldrich. 2020. "Operational state detection in hydrocyclones with convolutional neural networks and transfer learning." Minerals Engineering 149
• Aldrich, C. 2020. "Process variable importance analysis by use of random forests in a shapley regression framework." Minerals 10 (5)
• Ilankoon, N. D., C. Aldrich, E. A. Oraby, and J. J. Eksteen. 2020. "Use of polyethylenimine functionalised magnetic nanoparticles for gold thiosulfate recovery." Hydrometallurgy 195
• Ilankoon, N. D., C. Aldrich, E. A. Oraby, and J. J. Eksteen.. "Extraction of Gold and Copper from a Gold Ore Thiosulfate Leachate by Use of Functionalized Magnetic Nanoparticles." Mineral Processing and Extractive Metallurgy Review 41 (5). Inpress.

2019

• Ilankoon, N. D., E. A. Oraby, J. J. Eksteen, and C. Aldrich. 2019. "Gold adsorption and elution in thiosulfate leaching system using functionalized magnetic nanoparticles."
• Fu, Y., and C. Aldrich. 2019. "Flotation froth image recognition with convolutional neural networks." Minerals Engineering 132: 183-190.
• Krishnannair, S., and C. Aldrich. 2019. "Statistical process monitoring of a base metal flotation plant using a Gaussian mixture model and dissimilarity scale based singular spectrum analysis."
• Fu, Y., and C. Aldrich. 2019. "Quantitative Ore Texture Analysis with Convolutional Neural Networks."
• Kok, T. L., and C. Aldrich. 2019. "Analysis of Electrochemical Noise for Corrosion Type Identification by Use of Global Recurrence Plots and Texture Analysis."
• Aldrich, C., and J. Olivier. 2019. "Nonlinear Time Series Analysis of Avalanching Granular Flow Data."
• Krishnannair, S., and C. Aldrich. 2019. "Process Monitoring and Fault Detection using Empirical Mode Decomposition and Singular Spectrum Analysis."
• Yao, W. L., S. Mostafa, E. Ericson, Z. Yang, G. Xu, and C. Aldrich. 2019. "Enhancement of fluid flow performance through deep fractured rocks in an in-situ leaching potential mine site using discrete fracture network (DFN)." Geomechanics and Engineering 18 (6): 585-594.

2018

• Feng, C., C. Aldrich, J. J. Eksteen, and D. W. M. Arrigan. 2018. "Removal of arsenic from gold cyanidation process waters by use of cerium-based magnetic adsorbents." Minerals Engineering 122: 84-90.
• Mpinga, C. N., J. J. Eksteen, C. Aldrich, and L. Dyer. 2018. "A conceptual hybrid process flowsheet for platinum group metals (PGMs) recovery from a chromite-rich Cu-Ni PGM bearing ore in oxidized mineralization through a single-stage leach and adsorption onto ion exchange resin." Hydrometallurgy 178: 88-96.
• Fu, Y., and C. Aldrich. 2018. "Froth image analysis by use of transfer learning and convolutional neural networks." Minerals Engineering 115: 68-78.
• Hou, Y., C. Aldrich, K. Lepkova, and B. Kinsella. 2018. "Detection of under deposit corrosion in a CO2 environment by using electrochemical noise and recurrence quantification analysis." Electrochimica Acta 274: 160-169.
• Mpinga, C. N., J. J. Eksteen, C. Aldrich, and L. Dyer. 2018. "Atmospheric leach process of high-chromitite PGM-bearing oxidized mineralized ore through a single-stage and two-stage techniques." Minerals Engineering 125: 165-175.
• Feng, C., C. Aldrich, J. J. Eksteen, and D. W. M. Arrigan.. "Removal of arsenic from gold processing circuits by use of novel magnetic nanoparticles." Canadian Metallurgical Quarterly - Inpress.
• Aldrich, C., L. K. Smith, D. I. Verrelli, W. J. Bruckard, and M. Kistner. 2018. "Multivariate image analysis of realgar–orpiment flotation froths." Mineral Processing and Extractive Metallurgy: Transactions of the Institute of Mining and Metallurgy 127 (3): 146-156.
• Heunis, T., C. Aldrich, J. M. Peters, S. S. Jeste, M. Sahin, C. Scheffer, and P. J. de Vries. 2018. "Recurrence quantification analysis of resting state EEG signals in autism spectrum disorder - a systematic methodological exploration of technical and demographic confounders in the search for biomarkers." BMC Medicine 16 (1)
• Hou, Y., C. Aldrich, K. Lepkova, and B. Kinsella. 2018. "Identifying corrosion of carbon steel buried in iron ore and coal cargoes based on recurrence quantification analysis of electrochemical noise." Electrochimica Acta 283: 212-220.
• Fu, Y., and C. Aldrich. 2018. "Using Convolutional Neural Networks to Develop State-of-the-Art Flotation Froth Image Sensors." IFAC-PapersOnLine 51 (21): 152-157.
• Bardinas, J. P., C. Aldrich, and L. F. A. Napier. 2018. "Predicting the operating states of grinding circuits by use of recurrence texture analysis of time series data." Processes 6 (2)

2017

• Feng, C., C. Aldrich, J. J. Eksteen, and D. W. M. Arrigan. 2017. "Removal of arsenic from alkaline process waters of gold cyanidation by use of gamma-Fe2O3@ZrO2 nanosorbents." Hydrometallurgy 174: 71-77.
• Mpinga, C. N., J. Eksteen, C. Aldrich, and L. Dyer. 2017. "Identification of the significant factors determining extractability of Ni and Cu after sulfation roasting of a PGM-bearing chromitite ore." Minerals Engineering 110: 153-165.
• Hou, Y., C. Aldrich, K. Lepkova, L. L. Machuca, and B. Kinsella. 2017. "Application of electrochemical noise technique to monitor carbon steel corrosion under sand deposit." In NACE - International Corrosion Conference and Expo 2017, Mar 26, 2017, New Orleans, Loisiana, USA
• Napier, L. F. A., and C. Aldrich. 2017. "An IsaMill Soft Sensor based on Random Forests and Principal Component Analysis." IFAC-Papersonline 50 (1): 1175-1180.
• Feng, C., C. Aldrich, J. J. Eksteen, and D. W. M. Arrigan. 2017. "Removal of arsenic from alkaline process waters of gold cyanidation by use of Fe3O4@SiO2@TiO2 nanosorbents." Minerals Engineering 110: 40-46.
• Hou, Y., C. Aldrich, K. Lepkova, L. L. Machuca, and B. Kinsella. 2017. "Analysis of electrochemical noise data by use of recurrence quantification analysis and machine learning methods." Electrochimica Acta 256: 337-347.
• Krishnannair, S., and C. Aldrich. 2017. "Fault detection in the Tennessee Eastman benchmark process with nonlinear singular spectrum analysis." IFAC-Papersonline 50 (1): 8005-8010.
• Horn, Z. C., L. Auret, J. T. McCoy, C. Aldrich, and B. M. Herbst. 2017. "Performance of Convolutional Neural Networks for Feature Extraction in Froth Flotation Sensing." IFAC-Papersonline 50 (2): 13-18.

2016

• Hou, Y., C. Aldrich, K. Lepkova, L. Machuca Suarez, and B. Kinsella. 2016. "Monitoring of carbon steel corrosion by use of electrochemical noise and recurrence quantification analysis." Corrosion Science 112: 63-72.
• Bardinas, J., C. Aldrich, and B. Albijanic. 1468495656060. "Identification of the dynamic behaviour of an autogenous mill by use of time series cluster analysis."
• Brink, S., C. Dorfling, and C. Aldrich. 2016. "An acoustic sensor for prediction of the structural stability of rock." International Journal of Rock Mechanics and Mining Sciences 85: 187-191.
• Heunis, T. M., C. Aldrich, and P. J. de Vries. 2016. "Recent Advances in Resting-State Electroencephalography Biomarkers for Autism Spectrum Disorder-A Review of Methodological and Clinical Challenges." Pediatric Neurology 61: 28-37.
• Krishnannair, S., C. Aldrich, and G. T. Jemwa. 2016. "Detecting faults in process systems with singular spectrum analysis." Chemical Engineering Research and Design 113: 151-168.
• Fu, Y., and C. Aldrich. 2016. "Flotation Froth Image Analysis by Use of a Dynamic Feature Extraction Algorithm." IFAC-PapersOnLine 49 (20): 84-89.

2015

• Ngoie Mpinga, C., J. J. Eksteen, C. Aldrich, and L. Dyer. 2015. "Direct leach approaches to Platinum Group Metal (PGM) ores and concentrates: A review." Minerals Engineering 78: 93-113.
• Groenewald, J. W. D., and C. Aldrich. 2015. "Root cause analysis of process fault conditions on an industrial concentrator circuit by use of causality maps and extreme learning machines." Minerals Engineering 74: 30-40.
• Aldrich, C., F. D. L. Uahengo, and M. Kistner. 2015. "Estimation of particle size in hydrocyclone underflow streams by use of Multivariate Image Analysis." Minerals Engineering 70: 14-19.
• Aldrich, C. 2015. "Hydrocyclones." In Progress in Filtration and Separation Tarleton, S., 1-24 UK: Elsevier.
• Amankwah, A., and C. Aldrich. 2015. "Motion estimation in flotation froth using the Kalman filter." In 2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2015), Jul 26, 2015, Milan, Italy
• Amankwah, A., and C. Aldrich. 2015. "A spatial information measure method for hyperspectral image visualization." In 2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Jul 26, 2015, Milan, Italy

2014

• Phiri, M. J., and C. Aldrich. 2014. "On-line monitoring of aqueous base metal solutions with transmittance spectrophotometry." Minerals Engineering 61: 23-31.
• Aldrich, C., J. J. Burchell, J. W. D. V. Groenewald, and C. Yzelle. 2014. "Visualization of the controller states of an autogenous mill from time series data." Minerals Engineering 56: 1-9.
• Amankwah, A., and C. Aldrich. 2014. "Automatic flotation froth bubble size distribution estimation using mean shift and watershed transforms." In International Geoscience and Remote Sensing Symposium (IGARSS 2014) / 35th Canadian Symposium on Remote Sensing (35th CSRS), Jul 13, 2014, Quebec, Canada: IEEE.
• Aldrich, C., M. Kistner, L. Auret, D. Verrelli, L. Smith, and W. Bruckhard. 2014. "Grade estimation in realgar-orpiment batch flotation systems by froth image analysis and kernel methods." In XXVII International Mineral Processing Congress (IMPC 2014), Oct 20, 2014, Santiago, Chile: GECAMINI Digital Publications.
• Amankwah, A., and C. Aldrich. 2014. "Automatic estimation of bubble size distributions in flotation froths by use of a mean shift algorithm and watershed transforms." In 2014 IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2014), Jul 13, 2014, Quebec City, Quebec, Canada: IEEE.

2013

• Kistner, M., G. T. Jemwa, and C. Aldrich. 2013. "Monitoring of mineral processing systems by using textural image analysis." Minerals Engineering 52: 169-177.
• Shugman, E. M., C. Aldrich, R. D. Sanderson, and D. S. McLachlan. 2013. "Infrasonic backpulsed membrane cleaning micro- and ultrafiltration membranes fouled with alumina and yeast." Water SA 39 (1): 9-16.
• Aldrich, C. 2013. "Consumption of steel grinding media in mills - A review." Minerals Engineering 49: 77-91.
• Yang, X., and C. Aldrich. 2013. "Optimising control of coal flotation by neuro-immune algorithm." International Journal of Mining Science and Technology 23 (3): 407-413.
• Aldrich, C., and L. Auret. 2013. "Unsupervised Process Monitoring and Fault Diagnoses with Machine Learning Methods." London: Springer.
• Chibwe, D. K., G. Akdogan, C. Aldrich, and P. Taskinen. 2013. "Modelling of mixing, mass transfer and phase distribution in a Peirce-Smith converter model." Canadian Metallurgical Quarterly 52 (2): 176-189.

2012

• Amankwah, A., and C. Aldrich. 2012. "Motion Estimation in Flotation Froth Images Based on Edge Detection and Mutual Information." In 2012 32nd IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2012, Jul 22, 2012, Munich, Germany: IEEE.
• Amankwah, A., and C. Aldrich. 2012. "Multiresolution Image Registration Using Spatial Mutual Information." In OCEANS 2012 MTS/IEEE Hampton Roads Conference: Harnessing the Power of the Ocean, Oct 14, 2012, Virginia Beach Convention Centre, VA, USA: IEEE.

2011

• Amankwah, A., and C. Aldrich. 2011. "Automatic ore image segmention using mean shift and watershed transform." In 21st International Conference Radioelektronika 2011, Apr 19, 2011, Brno, Czech Republic
• Amankwah, A., and C. Aldrich. 2011. "Automatic ore image segmentation using mean shift and watershed transform." In 21st International Conference Radioelektronika 2011, Apr 19, 2011, Brno, Czech Republic

2010

• Aldrich, C. 2010. "Welcome letter."
• Jemwa, G., and C. Aldrich. 2010. "Estimating particle size fraction proportions - a multiscale approach using multiple kernel learning."
• Auret, L., and C. Aldrich. 2010. "Diagnostic monitoring of concentrator circuits with random forest models."
• Amankwah, A., and C. Aldrich. 2010. "Rock image segmentation using watershed with shape markers."

2009

• Aldrich, C., G. T. Jemwa, J. C. Van Dyk, M. J. Keyser, and J. H. P. Van Heerden. 2009. "Online analysis of coal on a conveyor belt by use of machine vision and kernel methods."
• Lorenzen, L., J. J. Eksteen, M. Pelser, C. Aldrich, and G. Georgalli. 2009. "Activated alumina-based adsorption and recovery of excess fluoride ions subsequent to calcium and magnesium removal in base metal leach circuits." Southern African Institute of Mining and Metallurgy. Journal 109: 447-453.

2007

• De Groenewald, J. W. V., C. Aldrich, J. J. Eksteen, A. V. E. Conradie, and L. P. Coetzer. 2007. "Simulated neurocontrol of an autogenous mill with evolutionary reinforcement learning."
• Aldrich, C., G. T. Jemwa, and S. Krishnannair. 2007. "Multiscale process monitoring with singular spectrum analysis."
• Engelbrecht, A. M., B. Bredenkamp, and C. Aldrich. 2007. "Simulation of fouling in membrane processes with cellular automata." Journal of the Southern African Institute of Mining and Metallurgy 107 (4): 225-229.
• Jemwa, G. T., and C. Aldrich. 2007. "Process fault diagnosis using one-class support vector machines."
• Aldrich, C., and G. T. Jemwa. 2007. "Detecting change in complex process systems with phase space methods."
• Wang, Q., and C. Aldrich. 2007. "Monitoring of a semi-autogenous grinding circuit on a gold plant with topology preserving projection methods and neural networks."
• Musee, N., L. Lorenzen, and C. Aldrich. 2007. "Modelling undissolved gold losses in an industrial plant with neurofuzzy methods."

2006

• Pelser, M., J. J. Eksteen, L. Lorenzen, and C. Aldrich. 2006. "The effect of mixing regimes on the precipitation behaviour of fluorite and sellaite from high ionic strength sulphate solutions."
• Lottering, J. M., and C. Aldrich. 2006. "Online measurement of factors influencing the electrostatic separation of mineral sands." Journal of the Southern African Institute of Mining and Metallurgy 106 (4): 283-290.
• Aldrich, C. 2006. "Process Systems '05." Minerals Engineering 19 (11)

2005

• Yang, X., and C. Aldrich. 2005. "Rheology of aqueous magnetite suspensions in uniform magnetic fields." International Journal of Mineral Processing 77 (2): 95-103.
• Jemwa, G., and C. Aldrich. 2005. "Automatic fault detection and identification with support vector methods."
• Gardner, S., N. J. Le Roux, and C. Aldrich. 2005. "Process data visualisation with biplots." Minerals Engineering 18 (9): 955-968.
• Yang, X. P., and C. Aldrich. 2005. "Detecting change in process systems with immunocomputing." Journal of Coal Science and Engineering 11 (1): 56-58.
• Le Roux, N. J., S. Gardner, and C. Aldrich. 2005. "Biplot analysis of process systems."
• Maree, C., A. J. Burger, and C. Aldrich. 2005. "The development of a standalone computer simulation tool for the optimization of gypsum recovery at Afmine." Journal of The South African Institute of Mining and Metallurgy 105 (3): 207-214.

2004

• Theron, J. P., and C. Aldrich. 2004. "Identification of nonlinearities in dynamic process systems." Journal of The South African Institute of Mining and Metallurgy 104 (3): 191-200.
• Feng, D., and C. Aldrich. 2004. "Adsorption of heavy metals by biomaterials derived from the marine alga Ecklonia maxima." Hydrometallurgy 73 (1-2): 1-10.
• Barkhuizen, M., and C. Aldrich. 2004. "Classification of process dynamics with monte carlo singular spectrum analysis." Computer Aided Chemical Engineering 18 (C): 565-570.

2003

• Jemwa, G. T., and C. Aldrich. 2003. "Identification of Chaotic Process Systems with Least Squares Support Vector Machines."
• Jemwa, G. T., and C. Aldrich. 2003. "Non-linear system identification of an autocatalytic reactor using least squares support vector machines." Journal of The South African Institute of Mining and Metallurgy 103 (2): 119-125.
• Barnard, J. P., and C. Aldrich. 2003. "Diagnostic Monitoring of Internal Combustion Engines by Use of Independent Component Analysis and Neural Networks."
• Aldrich, C., and M. Barkhuizen. 2003. "Classification of process dynamics with Monte Carlo singular spectrum analysis." Journal of The South African Institute of Mining and Metallurgy 103 (2): 127-137.

2002

• Aldrich, C. 2002. "Preface."
• Aldrich, C.. "Zinc removal from hydroxide precipitates by dissolved air flotation." Minerals Engineering 15(12) Inpress.
• Conradie, A. V. E., R. Miikkulainen, and C. Aldrich. 2002. "Intelligent process control utilising symbiotic memetic neuro-evolution."
• Qi, B. C., and C. Aldrich. 2002. "Effect of ultrasonic treatment on zinc removal from hydroxide precipitates by dissolved air flotation." Minerals Engineering 15 (12): 1105-1111.
• Aldrich, C., and J. P. Barnard. 2002. "Chapter 10 Embedding of multivariate dynamic process systems." Process Metallurgy 12 (C): 299-312.
• Aldrich, C., and J. P. Barnard. 2002. "Chapter 9 Case studies: Dynamic systems analysis and modelling." Process Metallurgy 12 (C): 285-298.

2001

• Barnard, J. P., C. Aldrich, and M. Gerber. 2001. "Embedding of multidimensional time-dependent observations." Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 64 (4)
• Aldrich, C.. "Embedding of multidimensional time-dependent observations." Physical Review E 64(4) Inpress.
• Feng, D., L. Lorenzen, C. Aldrich, and P. W. Maré.. "Ex situ diesel contaminated soil washing with mechanical methods." Minerals Engineering 14(8) Inpress.
• Barnard, J. P., C. Aldrich, and M. Gerber.. "Identification of dynamic process systems with surrogate data methods." AlChE Journal 47(9) Inpress.
• Chemaly, T. P., and C. Aldrich.. "Visualization of process data by use of evolutionary computation." Computers and Chemical Engineering 25(9-10) Inpress.
• Feng, D., and C. Aldrich.. "The influence of pulp pulsation on the batch flotation of galena." Chemical Engineering Communications 186 Inpress.
• Barnard, J. P., and C. Aldrich. 2001. "A systematic methodology for empirical modeling of non-linear state space systems." Computer Aided Chemical Engineering 9 (C): 75-80.
• Conradie, A. V. E., and C. Aldrich. 2001. "Neurocontrol of a ball mill grinding circuit using evolutionary reinforcement learning." Minerals Engineering 14 (10): 1277-1294.
• Barnard, J. P., and C. Aldrich. 2001. "Modelling of air pollution in an environmental system by use of non-linear independent component analysis." Computer Aided Chemical Engineering 9 (C): 81-86.

2000

• Feng, D., C. Aldrich, and H. Tan.. "Treatment of acid mine water by use of heavy metal precipitation and ion exchange." Minerals Engineering 13(6) Inpress.
• Feng, D., and C. Aldrich.. "A comparison of the flotation of ore from the Merensky Reef after wet and dry grinding." International Journal of Mineral Processing 60 Inpress.
• Aldrich, C., and D. Feng. 2000. "Removal of heavy metals from wastewater effluents by biosorptive flotation." Minerals Engineering 13 (10): 1129-1138.
• Els, E. R., L. Lorenzen, and C. Aldrich. 2000. "Adsorption of precious metals and base metals on a quaternary ammonium group ion exchange resin." Minerals Engineering 13 (4): 401-414.
• Feng, D., C. Aldrich, and H. Tan.. "Removal of heavy metals ions by carrier magnetic separation of absorptive particulates." Hydrometallurgy 56 Inpress.
• Feng, D., and C. Aldrich.. "Elution of ion exchange resins by use of ultrasonication." Hydrometallurgy 55(3) Inpress.
• Feng, D., and C. Aldrich.. "Batch flotation of a complex sulphide ore by use of pulsated sparged air." International Journal of Mineral Processing 60 Inpress.
• Aldrich, C.. "Removal of heavy metals from wastewater effluents by biosorptive flotation." Minerals Engineering 13(10-11) Inpress.
• Aldrich, C., and D. Feng.. "The effect of frothers on bubble size distributions in flotation pulp phases and surface froths." Minerals Engineering 13(10-11) Inpress.
• Feng, D., and C. Aldrich.. "REmoval of diesel from aqueous emulsions by flotation." Separation Science and Technology 35(13) Inpress.
• Aldrich, C.. "The adsportiion of precious metals and base metals on a quaternary ammonium group ion exchange resin." Minerals Engineering 13(4) Inpress.
• Aldrich, C., G. P. J. Schmitz, and F. S. Gouws.. "Development of fuzzy rule-based systems for industrial flotaion plants by use of inductive techniques and genetic algorithms." The Canadian Journal of Chemical Engineering 100(2) Inpress.
• Aldrich, C.. "Cluster analysis of mineral process data with autoassociative neural networks." Chemical Engineering Communications 177 Inpress.
• Feng, D., and C. Aldrich.. "Sonochemical treatment of simulated soil contaminated with diesel." Advances in Environmental Research 4(2) Inpress.
• Aldrich, C., and D. A. Theron.. "Acoustic estimation of the particle size distributions of sulphide ores in a laboratory ball mill." Journal of the South African Institute of Mining and Metallurgy 100(4) Inpress.
• Barnard, J. P., and C. Aldrich. 2000. "Detecting outliers in multivariate process data by using convex hulls." Computer Aided Chemical Engineering 8 (C): 103-107.
• Els, E. R., L. Lorenzen, and C. Aldrich. 2000. "The adsorption of precious and base metals on XAD7 ion exchange resin." Developments in Mineral Processing 13 (C)

1999

• Feng, D., and C. Aldrich.. "Effect of particle size on flotation performance of complex su;phide ores." Minerals Engineering 12(7) Inpress.
• Feng, D., and C. Aldrich.. "Effect of fluid porperties on two-phase froth characteristics." Industrial and Engineering Chemistry Research 38(10) Inpress.
• Aldrich, C., and M. A. Reuter.. "Monitoring of metallurgical reactors by the use of topographic mapping of process data." Minerals Engineering 12(11) Inpress.
• Aldrich, C., and D. Feng.. "Effect of ultrasonic preconditioning of pulp on the flotation of sulphide ores." Minerals Engineering 12(6) Inpress.
• Schmitz, G. P. J., and C. Aldrich.. "Combinatorial evolution of regression nodes for feedforward neural networks." Neural Networks 12(1) Inpress.
• Aldrich, C.. "An algorithm for extraction of decision trees from artificial neural networks." I E E E TRANSACTIONS OF NEURAL NETWORKS 10(6) Inpress.
• Schmitz, G. P. J., C. Aldrich, and F. S. Gouws. 1999. "ANN-DT: An algorithm for extraction of decision trees from artificial neural networks." IEEE Transactions on Neural Networks 10 (6): 1392-1401.

1998

• Aldrich, C. 1998. "Visualization of transformed multivariate data sets with autoassociative neural networks." Pattern Recognition Letters 19 (8): 749-764.
• Petersen, K. R. P., C. Aldrich, and J. S. J. Van Deventer.. "Analysis of ore particles based on textural pattern recognition." Minerals Engineering 11(10) Inpress.
• Aldrich, C.. "Visualization of multivariate data with autoassociative neural networks." Pattern Recognition Letters 19 Inpress.
• Greeff, D. J., and C. Aldrich.. "Development of an empirical model of a nickeliferous chromite leaching system by means of genetic programming." South African Institute of Mining and Metallurgy Journal (SAIMM) 98(4) Inpress.
• Greeff, D. J., and C. Aldrich.. "Empirical modelling of chemical process systems with evolutionary programming." Computers and Chemical Engineering 22(7-8) Inpress.
• Schmitz, G. P. J., and C. Aldrich.. "Neurofuzzy modelling of chemical process systems with ellipsoidal radial basis function neural networks and genetic algorithms." Computers and Chemical Engineering 22 Inpress.
• Petersen, K. R. P., and C. Aldrich. 1998. "Prediction of choking in hydrocyclones by use of elementary particle interaction theory." International Journal of Mineral Processing 53 (4): 201-211.

1997

• Els, E. R., L. Lorenzen, and C. Aldrich.. "The recovery of palladium with the use of ion exchange resins." Minerals Engineering 10(10) Inpress.
• Aldrich, C., D. W. Moolman, S. J. Bunkell, M. C. Harris, and D. A. Theron. 1997. "Relationship between surface froth features and process conditions in the batch flotation of a sulphide ore." Minerals Engineering 10 (11): 1207-1218.
• Aldrich, C.. "RElationship between surface froth features and process conditions in the batch flotation of a sulphide ore." Minerals Engineering 10(11) Inpress.
• Reuter, M. A., C. West, A. Fourie, D. W. Moolman, and C. Aldrich.. "The use of dimensionless numbers to characterise the feed to metallurgical reactors." Minerals Engineering 10(1) Inpress.
• Aldrich, C., D. W. Moolman, F. S. Gouws, and G. P. J. Schmitz. 1997. "Machine learning strategies for control of flotation plants."

1996

• Petersen, K. R. P., C. Aldrich, J. S. J. Van Deventer, C. McInnes, and W. W. Stange.. "Hydrocyclone underflow monitoring using image processing methods." Minerals Engineering 9(3) Inpress.
• Moolman, D. W., C. Aldrich, G. P. J. Schmitz, and J. S. J. Van Deventer.. "The interrelationship between surface froth characteristics and industrial flotation performance." Minerals Engineering 9(8) Inpress.
• Giles, A. E., C. Aldrich, and J. S. J. Van Deventer.. "Modelling of rare earth solvent extrraction with artificial neural nets." Hydrometallurgy 43(1-3) Inpress.
• Annandale, G. J., L. Lorenzen, J. S. J. Van Deventer, and C. Aldrich.. "Neural net alalysis of the liberation of gold using diagnostic leaching data." Minerals Engineering 9(2) Inpress.
• Moolman, D. W., J. J. Eksteen, C. Aldrich, and J. S. J. Van Deventer.. "The significance of flotation froth appearance for machine vision control." International Journal of Mineral Processing 48(3-4) Inpress.
• Van Deventer, J. S. J., D. W. Moolman, and C. Aldrich.. "Visualisation of plant disturbances using self-organising maps." Computers and Chemical Engineering 20 Inpress.
• Rademan, J. A. M., D. W. Moolman, L. Lorenzen, J. S. J. Van Deventer, and C. Aldrich.. "Neural net based knowledge extraction from the historical data of an industrial leaching process." Hydrometallurgy 43(1-3) Inpress.
• Gouws, F. S., and C. Aldrich.. "Rule-based characterization of industrial flotation processes with inductive techniques and genetic algorithms." Industrial and Engineering Chemistry Research 35(11) Inpress.
• Aldrich, C. 1996. "Intelligent systems and process engineering." South African Journal of Science 92 (7): 300-301.

1995

• Aldrich, C., D. Moolman, J. J. Eksteen, and J. S. J. Van Deventer.. "Characterization of flotation processes with self-organizing neural nets." Chemical Engineering Communications 139 Inpress.
• Aldrich, C., and J. S. J. Van Deventer.. "Modelling of induced aeration in turbine aerators by use of radial basis function neural networks." The Canadian Journal of Chemical Engineering 73(6) Inpress.
• van Deventer, J. S. J., S. P. Liebenberg, L. Lorenzen, and C. Aldrich.. "Dynamic modelling of competitive elution of activated carbon in columns using neural networks." Minerals Engineering 8(12) Inpress.
• Aldrich, C., D. W. Moolman, and J. S. J. van Deventer.. "Monitoring and control of hydrometallurgical processes with self-organizing and adaptive neural net systems." Computers and Chemical Engineering 19 (1) Inpress.
• Aldrich, C.. "The analysis of video graphic process data with neural nets." Acta Chimica Slovenica 42(1) Inpress.
• Aldrich, C.. "TGhe interpretation of flotation froth surfaces by using digital image analysis and neural networks." Chemical Engineering Science 50(22) Inpress.
• Moolman, D. W., C. Aldrich, J. S. J. van Deventer, and W. W. Stange.. "The classification of froth sturctures in a copper flotation plant by means of a neural net." International Journal of Mineral Processing 43(3/4) Inpress.
• Aldrich, C., and J. S. J. van Deventer.. "Hybrid connectionist modelling of the kinetics of thermal decomposition processes." Thermochimica Acta 257 Inpress.
• Aldrich, C.. "TGhe monitoring of froth surfaces on industrial flotation plants using connectionist image processing techniques." Minerals Engineering 8(1-2) Inpress.
• Aldrich, C., and J. S. J. van Deventer.. "Comparison of different artificial neural nets for the detection and location of gross errors in process systems." Industrial and Engineering Chemistry Research 34(1) Inpress.
• Moolman, D. W., C. Aldrich, and J. S. J. Van Deventer. 1995. "The monitoring of froth surfaces on industrial flotation plants using connectionist image processing techniques." Minerals Engineering 8 (1-2): 23-30.
• van Deventer, J. S. J., C. Aldrich, and D. W. Moolman. 1995. "Tracking of changes in chemical processes using computer vision and self-organizing maps."
• Moolman, D. W., C. Aldrich, J. S. J. Van Deventer, and D. J. Bradshaw. 1995. "The interpretation of flotation froth surfaces by using digital image analysis and neural networks." Chemical Engineering Science 50 (22): 3501-3513.

1994

• Moolman, D. W., C. Aldrich, J. S. J. Van Deventer, and W. W. Stange.. "Digital image processing as a tool for on-line monitoring of froth in flotation plants." Minerals Engineering 7(9) Inpress.
• Aldrich, C., J. S. J. Van Deventer, and M. A. Reuter.. "The application of neural nets in the metallurgical industry." Minerals Engineering 7(5-6) Inpress.
• Aldrich, C., and J. S. J. van Deventer.. "The use of connectionist systems to reconcile inconsistent process data." Chemical Engineering Journal 54(3) Inpress.
• Aldrich, C., and J. S. J. van Deventer.. "Observations on induced aeration in agitated slurries." Chemical Engineering Journal and the Biochemical Engineering Journal 54(3) Inpress.
• Aldrich, C., and J. S. J. Van Deventer.. "Identification of gross errors in material balance measurements by means of neural nets." Chemical Engineering Science 49(9) Inpress.
• Aldrich, C., and J. S. J. van Deventer.. "Observations on the effect of medium viscosity and density on the rate of induced aeration in agitated vessels." Metallurgical and Materials Transactions B 25B Inpress.
• Aldrich, C., and J. S. J. Deventer. 1994. "Observations on the effect of medium density and viscosity on the rate of induced aeration in agitated vessels." Metallurgical and Materials Transactions B 25 (2): 303-306.
• Aldrich, C. 1994. "XV CMMI Congress. Sun City, South Africa, 4-9 Septemner 1994."

1993

• Aldrich, C., and J. S. J. van Deventer.. "The use of neural nets to detect systematic errors in process systems." International Journal of Mineral Processing 39 Inpress.
• Aldrich, C., M. A. Reuter, and J. S. J. Van Deventer. 1993. "Artificial intelligence in process engineering." In Measurement, Control, and Optimization in Mineral Processing Glen, H. W., 123-156 Johannesburg, South Africa: South African Institute of Mining and Metallurgy.

1992

• Craig, B. D., T. F. Ferg, and C. Aldrich. 1992. "Corrosion/wear of titanium against steel in water and oil base drilling muds."
• Craig, B. D., T. E. Ferg, and C. Aldrich. 1992. "Corrosion/wear of titanium against steel in water and oil base drilling muds."

1991

• Ferg, T., B. D. Craig, and C. Aldrich. 1991. "Degradation of titanium drill pipe from corrosion and wear in a drilling environment." Society of Petroleum Engineers of AIME, (Paper) SPE