Dundee goes clean and green

The Dundee Precious Metals (DPM) smelter in Tsumeb is one of the few in the world that can handle complex gold-copper concentrates. The company expects the demand for the smelting of complex concentrates to increase as the demand for copper increases while ore grades decline.

Copper demand is set to grow as it is critical for enabling the energy transition. A wide variety of clean energy generation and storage technologies such as solar photovoltaics, wind turbines, geothermal energy and electric vehicles require significant amounts of copper.



Going solar

Dundee’s Tsumeb smelter has made a significant shift to renewable energy, according to the Canadian listed multinational.

In February, it announced that it had signed a five-year power purchase agreement with Alpha Namibia Industries Renewable Power (ANIREP) for at least 18.5 megawatts (MW) from its new N$300 million solar power plant near Keetmanshoop in southern Namibia.

Beginning in 2024, the consumption of renewable energy will cover approximately 30% of total electricity consumption at the smelter, and will lead to a significant decrease in harmful emissions, according to Dundee.



Watch the water

Another key performance indicator in Dundee’s balanced score card (BSC) approach to sustainable management of its Tsumeb smelter is water, with the focus on reducing freshwater consumption. Unfortunately, in 2022, a production issue at the smelter led to a major drop in output, causing Dundee to miss its corporate freshwater goal.

“We continue to invest in the improvement of the water infrastructure at our Tsumeb smelter. The renovation of storm-water channels will continue into 2023, together with a project to divert storm-water around the smelter,” which will further alleviate the water overflow issue, the company said in its 2022 sustainability report.

The Tsumeb smelter is in a high water stress area, so numerous measures to minimise water use have already been taken. For example, the water stored in the pollution control dam is reused in the slag mill facility.

“We have continuously implemented an extensive surface water management programme, including refurbishment of existing water canals, construction of new water canals, bunds and sumps, and construction of a pollution control dam for oil and water separation systems, pipelines and drainage spines.

"DPM’s holistic approach has resulted in a more than 40% reduction in the freshwater use intensity compared to 10 years earlier. Despite our progress in water management, issues with water overflows in the process plant are still present so we continue with our ambitious water infrastructure projects in 2023,” the organisation said.



Plants can clean

In Tsumeb, there is significant contamination of soil on-site, due to over a century of historic emissions from industrial-scale mining and smelting, augmented by spillages and wind erosion of tailings, slags and other wastes. The contaminants include a range of metalloids, metals and salts.

Clean-up and rehabilitation measures include both physical removal of spillage and eroded waste, and a range of plant and microbe-based technologies.

Collaborating with the University of the Witwatersrand, Dundee aims to improve the environment using plants with an ability to tolerate and remove specific pollutants. The white-flowered desert tamarisk (tamarix tamaricaceae) was selected as the most appropriate tree species for this process.

To promote vegetation growth on the tailings at Tsumeb, organic garden refuse is stored and transported to a dormant tailings facility.



Managing arsenic

Meanwhile, the processing of complex concentrate at the Tsumeb smelter results in hazardous arsenic-bearing dust. Since its acquisition in 2010, Dundee has mitigated the risk of contamination by storing arsenic waste in a hazardous waste landfill facility, purpose-built for this function.

The site is licenced by the government and is regularly inspected by third-party auditors, according to Dundee.

“We are mindful that we need to look beyond our current disposal methods and find solutions that provide us with a competitive advantage in the processing of arsenic-bearing complex concentrate. In 2022, we started a research project on the potential of storing arsenic at one central place and using it as ? regenerative energy carrier,” Dundee said.

During the smelting process, arsenic is captured in a specialised ‘drop box’. Last year, the company kick-started a project which aims to continuously remove the dust generated in the ‘drop box’, which contains about 30% arsenic, and prevent dust escaping. The plan is to install a combination of pumping, piping, screening and thickening systems which will wash the dust and process it in a wet form in the filter plant, it said.

In the past three years, Dundee has managed to reduce arsenic exposure in Tsumeb and achieve a 20% reduction compared to five years ago, despite a slight increase in 2022.

“We are now much closer to our target of 0.01mg/m3 under our company's arsenic exposure standard. Decreasing arsenic levels is part of our Tsumeb smelter's yearly BSC targets,” the sustainability report read.

Possibilities for regenerating the elemental arsenic by use of green energy or renewable fuel such as hydrogen and ammonia are being explored, as well as generating heat through arsenic combustion in fully enclosed vessels with oxygen, and using arsenic alloys in liquid metal batteries.

To drive continuous improvement, Dundee has developed an arsenic exposure reduction plan which focuses on engineering controls to limit emission generation. The arsenic exposure of DPM employees is strictly monitored.

An independent technical party verifies the environmental monitoring data. Dundee has also established an arsenic advisory panel, made up of an external group of global technical arsenic management experts.



Clean slag

At Tsumeb, Dundee is treating the site’s blast furnace slag - which is legacy from the blast furnace operation in earlier years - as a resource stockpile. Last year, the company performed a study for extracting the numerous valuable minerals contained in the stockpile. Some tests at pilot plant scale indicated good recovery of minerals in a pyro-metallurgical fuming process.

Additional, test work has been performed on reducing the residual waste, generating clean slag and an alloy. The clean slag has been tested with very good results, making it a potential resource for industrial uses such as concrete aggregate, a cement enhancer, among other things.

This means the elements of value can be reprocessed or sold. By doing so, it is expected that this process could cover the cost of the additional reduction step. Several options are currently under investigation to determine the most cost-efficient way to maximise mineral extraction and clean the slag in an environmentally responsible manner, Dundee said.



General waste

General waste such as plastic and papers is collected separately in the plant and administration offices and transported to a consolidation area. From there, the waste is sent off-site to registered recyclers and a safe disposal certificate is issued.

In the past year, the consolidation area has been improved while the construction of a new general waste facility is nearing completion.

The new general waste facility will include a recycling facility for sorting, baling, storing and dispatching, as well as an interim storage for non-arsenic hazardous waste and a disposal facility with a water containment pond.

Other waste such as old tyres are taken to an on-site consolidation area, and some are repurposed for demarcating mobile equipment parking on a small scale.

Furthermore, scrap metal generated from maintenance and repairs is transported to the consolidation area's scrap yard by skip truck. A scrap dealer sorts and packs the materials based on their metal type for off-site transportation and recycling purposes.