Acid leaching in chloride environment: the technology that will challenge large traditional sulphide concentration projects

José Miguel Ortiz, Mining Development Manager

In recent years we have witnessed a great and sustained advance in acid leaching technology in a chloride environment, driven among others by developments in Minera Michilla, Minera Tres Valles, Minera Spence, Minera Zaldívar, to name a few.

These projects, which attractively resolve the balance between capital investment, operating costs and profitability, have very successfully managed to move from traditional oxide leaching operations to an operation that allows the leaching of mixed, secondary and transitional sulphides (bornites), with quite competitive extraction levels.

The key variables of the process; the injection of salt, the type of salt, in what form it is introduced into the process, the rate of addition, the incorporation of resting stages, the injection of air into the piles, the changes in materiality and the control of chlorine drags in SX, have undoubtedly been an interesting development that allows this technology to prevail quite easily compared to the traditional grinding-flotation processes.

However, this has not stopped there: today the efforts of large companies, particularly in Chile, are to find the hydrometallurgical recipe for the immense reserves of primary sulphide’s that have not yet made the investment decision. A large part of the metallurgical laboratories, universities and both medium and large mining companies in Chile are in a race to develop a formula for their customers that allows their industrial implementation. In recent years, there has been a lot of optimism that in the short or medium term, hydrometallurgical options for chalcopyrite minerals will be developed industrially through chloride leaching with the incorporation of moderate temperature into the leaching cycle.

This is very good news. It is important for the entire copper industry to incorporate technological improvements that challenge the status quo and allow us to solve the great and urgent challenges. The challenges of copper mining are immense and already much discussed, including the depletion and low grades of resources, high operating costs, high energy and water consumption, environmental impacts, land use, among others.

Today, the most optimistic metallurgists are talking about a breaking point of around 65% copper extraction, that is, if the chlorinated leaching process with temperature reaches this level of efficiency in a controlled manner, it will be equivalent in profitability to a process via traditional concentration. This has already been achieved at the laboratory level and leaching in industrial columns and piles, so today the challenge is to scale these results to the industrial level in a stable and controlled manner. 

The technological problem of raising the temperature of heap leach solutions is a developing topic. Today, the energy options available in the north of our country have clearly opened with the incorporation of NCRE into the energy matrix. There are exciting developments in thermal technologies that will allow us to heat high volumes of solutions and air to inject them into the batteries. Therefore, the important thing is to open competition and develop this with clear and focused impulses. 

The traditional path of developing projects for the exploitation of copper sulphides with grinding-flotation technologies, and their subsequent melting of concentrates and electrorefining, will be strongly challenged in the coming years. This, fundamentally due to the more efficient use of energy, water and territory.

Will acid leaching in a chloride environment solve the age-old challenge of chalcopyrite leaching?

Pares & Alvarez believes so, sooner than many may think, and it will be done in Chile. It will be in our country, since there is already an important mobilization of companies in search of their optimization, there is the know-how and important human capital associated with this area of mining, and this technology solves essential aspects of many companies of their operations and projects, including:

• Low investment costs for retrofitting current hydrometallurgical plants
• Low operating costs, consumption of NaCl 10 -15 kg/ts, abundant national input in the north of Chile.
• Lower energy usage 5-10 KWh/t v/s 30 to 40 KWh/ts for concentrators.
• Low water consumption 0.15-0.18 m3/ts v/s 0.6 m3/ts (up to 1.0^m3/ts in the Central Zone)

It does not generate tailings deposits or dams, only 8% moisture rubble dumps

• It eliminates the problems associated with copper smelters such as sulfur dioxide and arsenic emissions.

This technology represents an enormous advantage for operations that transition from the leaching of oxides to sulphide’s, allowing the greater use of their facilities, making marginal resources profitable and the postponement of mine closures.

In short, acid leaching in the chloride environment is a great technological bet that proposes a relevant improvement in reducing capital investment and operating costs, which clearly has a better environmental assessment and that summons many mining operations and many professionals in Chile.