The transportation of material from a mining site, over vast distances, to a port terminal and beyond, is a crucial function in the mining value chain of any mining operation. The quality of the material delivered to the market is a key element to a successful operation. Risk management is reliant on product reconciliation and governance, ultimately enabling the determination and analysis of product variances in the mining sequence.

Figure: Material Flow

Bauxite Production

The graph below presents bauxite production by geographical location, measured in 1000 Metric Tons, as per the ‘Global bauxite production 2011-2021’ published by Statista in 2022. Guinea is the third-largest bauxite producer in the world.

Figure: Major bauxite producing countries in 2021

Primary Aluminium Production

Primary aluminium is the product of electrolytic reduction of metallurgical alumina and excludes recycled aluminium. The interpretation of the production of primary aluminium refers to the quantity of the molten liquid that is transferred to a holding furnace before further processing takes place.

Bauxite is mainly used to produce aluminium but is also used in other industries including (amongst others) the refractory, abrasive, cement, steel, and petrol industries.  Several processes are involved in the extraction of aluminium from bauxite including the Bayer Process and Hall-Heroult Process.  Once extracted, aluminium and aluminium-based alloys are used extensively in electronics, construction, vehicles, and even in tools and household utensils.

Conversion Factors

In 2018, the International Aluminium Institute reported that approximately 93% of alumina is used in the production of aluminium, and only a small proportion is used in the alumina chemicals industry, also known as the Speciality Alumina Market. The most widely used downstream specialty markets include the ceramics field, insulators and refractories, abrasives, absorbents, cements, and catalysts.

The graph presents the distribution of alumina used for aluminium production (93%) and other industry usages (7%).

Graph: Distribution of alumina

VBKOM Study

In April 2021, VBKOM had the opportunity to conduct a quality audit on a bauxite mine located in the Republic of Guinea in West Africa.

VBKOM was appointed to investigate product quality variances observed from pit to port in the mining value chain. VBKOM investigated the operation from a geological, mining, and metallurgical reconciliation point of view to determine and analyse the product quality variances observed by our client. VBKOM tackled this challenge eagerly and provided recommendations for improving product reconciliation to optimise the operation and enable continued success.

INVESTIGATING THE OPERATION

VBKOM conducted the following investigations into the West African operation:

• Review of geological block models with specific reference to the data collection, appropriateness of the sample collection method, and data interpretation and modeling;
• Review of the current grade control practices during mining and transport of material to the plant;
• Review of the Short Term Mine plan and the execution of the plan;
• Review of the sources of the material, both spatially and volumetrically, that compose the cargo of the ocean-going vessel, and provide an opinion on the grade predictability;
• Review of the full logistics chain to determine the origin of the quality issues and how to prevent them in the future;
• Review of the sampling process at the process plant and at the port out-load sampler for appropriateness and the execution;
• Review of the mining strategy and methods employed by our client;
• Review of the stockpile reclamation strategy at both the mine and port;
• Conduct a site visit in order to review the process in real-time

Image: Mining Site

Approach to the Investigation

The technical investigation was led by VBKOM’s Paul Obermeyer (Principal Geologist) and Mientjie van der Vyver (Principal Metallurgist) with specific interest in the following areas:

• Mine to Stockyard;
• Stockyard to Port;
• Port Stockyard to Barge.

The focus of the VBKOM study was to investigate general concerns regarding the flow and integration of data used for quality control and quality assurance processes.

The site visit to the mining operation required a holistic approach and included investigation of the sampling methodologies used throughout the production process, grade control practices, mining strategies, mine planning methodologies, and standards and execution. The visit to the port included a review of the material blending and sampling methodologies at the stockyards and during transport onto the barges.

Further investigation of the logistics quality assurance and quality control included:

• Plant logistical chain;
• Port logistical chain;
• Pit-to-Port tracking.

Image: Stockyard to Rail

Improving Quality

The main conclusions and recommendations from a geological, mining and logistical point of view included the following:

Geology:

• Frequent communication between the Geology Department and the Mineral Resource Geologist to prove reasonable correlation of grade with observed bauxite colour changes. Regular team interaction would improve the ability and confidence of the Grade Control Geologist to allocate material as required;
• Changing the sampling method to improve the integrity of the sampling data;
• Adding additional rock breakers to the mining fleet for boulder comminution prior to transport to the primary crusher for timeous processing.

Mining:

• Refining the Bottom of Mine depth estimates to allow for practical equipment selection by the planning department;
• Develop a planning standard for mining solids to assist grade predictability.

Logistics:

• Perform bias testing on sampling circuits to identify deviations timeously and limit quality related issues;
• Implementation of an Integrated Management System (IMS) to allow mitigation of quality control errors by human intervention.

Beyond the Port

Bauxite is the world’s main source of aluminium. VBKOM acknowledges and supports our clients’ commitment to operational quality in order to maximise this precious and finite world resource.

Sources:

• Byju’s 2020, accessed 6 April 2022, <https://byjus.com/chemistry/occurrence-and-extraction-of-aluminium/>
• ScienceDirect 2021, accessed 6 April 2022, <https://www.sciencedirect.com/topics/materials-science/alumina-production>
• Statista 2022, accessed 22 March 2022, <https://www.statista.com/statistics/799538/>
• International Aluminium Organisation February 2022, accessed 7 April 2022, <https://international-aluminium.org/statistics/primary-aluminium-production/>
• International Aluminium Organisation February 2022, accessed 7 April 2022, <https://international-aluminium.org/statistics/alumina-production/