Optimising electrowinning operations

by Dr Mark Cooksey

Optimising electrowinning operations to meet demand

Increasing current density without compromising quality

The increasing demand for base metals represents an opportunity for base metal producers around the globe. In today’s increasingly competitive environment, metal producers need to investigate options for increasing electrowinning production if they want to remain competitive and profitable.

For base metal electrowinning operations, it’s well known that increasing current density will result in increased metal production. However, managing the associated risks is not always straightforward.

Despite the increase in the number of sites running high current densities, a vast number of tank houses globally are still running low current densities. This is often due to an inability to assess, prepare for and control the associated risks, which makes increasing current density seem too difficult.

But if your operations aren’t expanding in line with market demands, you may find yourself left behind. Essentially, an inability to make changes to your core processes will restrict your production growth and lead to potential revenue losses.

Preparing to implement changes

Before undertaking operational changes, it’s important to identify, test and understand the various parameters and flow-on impacts of any change. This requires data collection, analysis, testing and interpretation in a controlled environment. Improved understanding will enable producers to increase electrowinning production without compromising product quality.

Prior to implementing new or optimised electrowinning operations, you need to consider:

• upstream and downstream processes, which are highly site-specific
• tank house challenges
• how to undertake testing in a controlled environment and de-risk implementation.

So, how do you overcome these challenges to stay competitive?

Potential risks of increasing current density

Electrowinning conditions vary significantly between different operating sites. You need to understand the site-specific factors that will influence production capabilities and site safety before embarking on process improvement. These factors can include upstream and downstream processes, electrolyte compositions, rectifier capacity, and current tank house design and its associated infrastructure.

Your ability to control these factors needs to be quantified when developing optimisation processes. If you attempt to increase current density without a strong understanding of the base-line parameters, you risk compromising your product and site safety by creating process disruptions and undesirable by-products. Not having the right measures in place or the necessary expertise can ultimately limit your site’s capacity to achieve production goals.

Tank house challenges include:

• Cathode metal quality — there is a strong belief and associated concern that an increase in current density will result in lower or compromised cathode metal quality. A lower quality product ultimately leads to compromised revenue.
• Short-circuits — when current density increases, metal can deposit non-uniformly or dendritically, and touch the opposite side of the plate. This can cause an electrical short circuit and compromise the entire tank cell(s).
• Electrical efficiency — increasing current density can result in lower current efficiency, due to energy losses and other variants that compromise output.
• Acid mist — higher current density leads to increased acid mist, compromising the safety of workers and accelerating the corrosion of equipment.
• Electrolyte impurities — at higher current densities, the effect of metallic and other impurities is exacerbated due to increased electrolyte flow rates and hydrodynamic effects within the cell. This can decrease the limiting current density, current efficiency and cathode metal quality.
• Anode wear  — increased current density can increase anode wear, but the benefit of increasing production often outweighs this cost.

The extent to which these physical and procedural barriers impede optimisation processes can vary. This is due to the different designs of tank houses across operations, and the processing steps which cause varying electrolyte compositions.

These challenges can make it difficult for base metal producers to increase production without having to compromise additional processes. Often, specialised knowledge and test equipment is needed to address these issues.

Engaging experts to optimise electrowinning operations

Do you have the required electrochemistry, fluid flow characterisation and modelling expertise to make the right decisions without compromising product quality or site safety? Increasing current density by trial and error carries the risk of disrupting your entire operation.

The most effective way to guarantee successful improvements is to engage experienced and knowledgeable professionals. This allows for process audits and pilot testing, ensuring the most efficient optimisation process can be evaluated and tailored to your site’s specific requirements, before you invest in a new process.

Market needs and ore grades will only continue to change. The ability to implement appropriate process improvements will ensure your business is able to keep up with demand both now and into the future.

CSIRO’s Mobile Electrowinning Pilot Plant offers an all-in-one solution

In addition to our expertise in multiphase flow characterisation, electrochemistry and electrical connections to reduce energy use, we have the capacity to optimise existing electrowinning operations, as well as test new equipment designs

To address the site-specific requirements, CSIRO has developed a Mobile Electrowinning Pilot Plant. Housed in a shipping container for transportation ease, the plant enables CSIRO to work closely with operators to test the efficacy of their electrowinning process on-site, using their electrolyte to deliver a customised solution. It provides an opportunity to trial various methodologies and techniques to increase current density and improve the mass transfer within a transparent electrowinning cell. This includes characterising bubble behaviour and acid mist, with the aim to increase cathode metal production without compromising quality.

The plant serves many functions, including the ability to:

• troubleshoot tank house issues over a single or several harvest cycles
• quantify total acid mist
• test various conditions and 3^rd party products (chemical additives and physical devices) that would aid to achieve higher current densities and/or reduce acid mist
• provide a rectified power supply capable of delivering up to 1000A/m² current density
• be transported to any site.

We have worked successfully with a number of companies to improve production without costly disruption of their electrowinning operations.

CSIRO’s expertise, facilities and extensive research capabilities can be leveraged to increase productivity, improve the financial return of mineral and metal production operations, and drive improved social and environmental outcomes.

Contact the CSIRO Mineral Resources Optimisation team on +61 3 9545 8865 or email me, Mark.Cooksey@csiro.au to talk about how we can work together on your next project.