Kinetics of lime dissolution in neutralisation of acid mine drainage

More from the Minerals to Metals Symposium 2016

Kinetics of lime dissolution in neutralisation of acid mine drainage
Acid mine drainage (AMD) contains high concentrations of dissolved heavy metals and sulphates, with pH values as low as 2.5. This can be toxic to plant and aquatic life, it is thefore important to treat acidic effluents before being discharged to the environment. AMD treatment involves neutralisation process, where AMD is reacted with alkaline solution to adjust pH to acceptable environmental standards. During neutralisation process, iron and other metals are removed or recovered in a form of oxides or oxyhydroxide precipitates.
Lime is a prefered neutralising agent because of it’s reactivity and accessibility. Beside lime’s potential benefits, it’s neutralisation fuction is reported as a very complicated task especially when high efficiency is targeted. This study therefore seeks to establish a rigorous analysis on lime dissolution kinetics in the context of South African AMD neutralisation. This is to be achieved through emperical models or established mathematical based models, labolatory studies such as the effect of dissolution of lime in a stirred tank under different conditions such as temperature, pH and concentration of different cations are to be explored.

This will then provide more value for the successive studies on the formation of iron precipitates and other metal recovery during lime neutralisation.
Senzo Mgabhi
MSc Chemical Engineering
“Other than deeper interest in water treatment, hydrometallurgy and chemical engineering science, Senzo is passionate about environment, nature conservation and sustainable development. As a Chemical Engineer, with attained analytical skills and growing aptitude in critical thinking, he seeks to pitch the sustainable solutions that are ethical, safe and environmental friendly.”

Two stage separation process for the management of sulfide wastes and associated ARD risks
The beneficiation of coal for down-stream use generates large quantities of solid waste, including overburden, discard and ultra-fine tailings. These wastes contain sulfide minerals, particularly pyrite, which oxidize and give rise to acid rock drainage (ARD), a major source of ground and surface water pollution.

Current attempts are focused on end-of-pipe technologies such as carbon capture and storage, clean coal combustion technologies, mining operations and control of pollution. Very little emphasis has been placed on opportunities related to use or recycling of downstream wastes. Sustainability through resource conservation and recycling is a growing field of research and development in which recent researchers have demonstrated the benefits of the principles of sustainability in contrast to the current end-of-pipe approaches.

Previous studies at the University of Cape Town in South Africa have demonstrated the technical feasibility of using froth flotation for separating pyritic sulphur from coal ultrafines in a two-stage process, which is aimed at simultaneously eliminating ARD risks and recovering valuable coal. In all case studies investigated to date, desulfurization flotation of base metal sulfide and coal processing wastes resulted in a sulfide-lean tailings which is non-acid generating thus effectively eliminating long-term ARD risks.

Juarez Amaral Filho
Postdoctoral Fellow
“Environmental engineer with PhD in Mineral and Environmental Technology at UFRGS – Brazil. Currently researching under the supervision of Prof. Harrison and Prof. Broadhurst, as a post-doctoral fellow. His research interests are environmental issues related to characterization, processing, discard and disposal of minerals wastes and effluents; mineral waste recycling and water reuse; and, ARD prediction, minimization and mitigation.”

UCT urban mine-understanding the local context to e-waste processing
Printed circuit boards (PCB’s) from end of life electronic waste (e-waste) contain significant quantities of metals. Some of these can be recovered profitably (extracting positive value) while others can become a hazard to the environment and humans if not disposed of appropriately (reducing negative value). High grade PCB’s are attractive to e-waste exporters, who because of the nature of the local industry, have the option to cherry pick these leaving behind low grade PCB’s with a low positive value or even negative value.

There is a need to develop and test process flow sheets that lead to optimal extraction of positive value and the responsible disposal of benign waste streams in the treatment of low and mixed grade PCB’s. The process flow sheets must be suitable for adaptation by emerging economies where energy costs, and availability of infrastructure, as would be required for a blast furnace operation, are a primary consideration.

A multi-stage hydrometallurgical treatment process, in which whole and cut up unpopulated PCB’s are processed is to be developed and tested. In this proposed process, low grade PCB’s (usually not multi-layered) go into sequential chemical baths, dissolving different groups of metals at each stage. The remaining substrate can then be sent out for further recycling. Economic and feasibility studies of the processes flow sheets at small to medium scale plants will be investigated.
Thandazile Moyo
Postdoctoral Fellow
“To laugh often and love much; to win the respect of intelligent persons and the affection of children; to earn the approbation of honest citizens and endure the betrayal of false friends; to know even one life has breathed easier because you have lived—this is to have succeeded.”- Ralph Waldo Emerson


Minerals To Metals Symposium 2016

Acid mine drainage

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