Producing iron ore for the direct-reduced iron market

If you or the company you work for are considering developing a new iron ore project or modifying an existing one to produce DR-grade concentrate, here are four challenges you may encounter and should prepare for.

Iron and silica liberation sizes will dictate the necessary magnitude of grinding power and the type of equipment that will be required for handling and dewatering flotation products. This parameter will have a direct impact not only on the project’s CAPEX and OPEX, but also on the project’s technical complexity, depending on its location, available concentrate and tailings storage, and transport infrastructure.

With a decreasing average particle size, the flowability and permeability of bulk solids typically deteriorate and their saturation moisture content increases. This can pose challenges for filtration, where either more time, more surface or more energy will be required to achieve the targeted residual moisture content, compared to coarse material filtration. It can also be problematic for tailings management, where dam construction and storage strategies sometime rely on the use of coarse material or on timely drainage of certain areas. With fine particles, dust emission can also become an issue and requires dust control measures to be put in place, which would also impact the project’s bottom line.

The availability of power may also pose some challenges, depending on the project’s location and the capacity of the existing local electrical infrastructure. Knowing the maximum power available for the project can help determine whether power will be a constraint when selecting a grind size for your processes or whether electrical upgrades will need to be included in the project’s scope and timeline.

The presence of other iron-bearing or high-density minerals in the deposit can also present some challenges. For example, iron-bearing silicates and hydroxides have shown poor response to conventional reverse flotation where starch is used as an iron depressant. This is because starch tends to be adsorbed by these minerals, which then end up in the concentrate stream, diluting the grade achieved. If a large portion of your resource has a high content of these minerals, it may be difficult to consistently achieve DR-grade concentrate quality with conventional reverse flotation reagent schemes. Therefore, alternative avenues should be investigated.

Reagents are not typically used in gravity and magnetic concentration plants but will be required if a flotation circuit is considered in the flowsheet of a given project. Some of the reagents often used in reverse flotation are known to be toxic to the environment, carcinogenic and/or corrosive. Some of these reagents are also the object of upcoming regulations in certain countries. Depending on the project’s location and context, some of these risks may be easy to mitigate, but others may require significant investment. These factors should be taken into consideration early in the project to select the reagents that will provide the best overall solution.

Securing the supply of these reagents should also be addressed sooner rather than later, especially if the potential project is in a remote location. For example, starch, which is often used as an iron-oxide depressant, is currently in shortage on the market due to a high demand for the food industry and a decrease in supply due to adverse weather conditions and the war in Ukraine.

In the past, if testwork has often been a bottleneck in project development, it is doubly true now. With the rising demand for DR-grade iron, many development projects are underway, and laboratories have very low availability. If your project is schedule-driven and has a high chance of going on to construction, plan for the entirety of the testwork that will need to be completed at project start-up to secure laboratory time and prevent long wait times between testwork phases. Be aware that parallel engineering may be required if time is short.

Testing new flotation technologies should also be carried out at the beginning of the project before engineering is too advanced. Several technologies exist now, beyond flotation cells and columns, and the potential to use any of them in your project should be assessed. Many of these new solutions have already been installed and their potential has been proven in the industry, so many subject matter experts and executives will expect these options to be considered in any flotation project going forward.

Determining the feasibility of a given project to produce high quality iron can be challenging. The first elements to review as part of that assessment are:

• Iron oxide and silica liberation sizes
• Presence of complex iron-bearing and high-density minerals
• Access to power and water
• Access to and location of concentrate and tailings storage infrastructures

If a review of these elements indicates favourable conditions, careful testwork planning will be required and should include:

• The comparison of several reagent schemes and their impact on metallurgical performance, effluent toxicity, health and safety risks and market availability
• The comparison of conventional and alternative flotation technologies

Foreseeing challenges related to these elements enables better planning and minimal disruptions to project progress and tackling them is an opportunity to make a positive impact in the years to come.