JOHANNESBURG (miningweekly.com) – Advanced water treatment company Miwatek has optimised its acid mine drainage (AMD) treatment technology to create a zero-liquid discharge process that only uses a single stage of reverse-osmosis (RO) processing.

The company, along with its partner in the venture – mining solutions company Fraser Alexander – successfully demonstrated this optimised process at its Randfontein pilot plant, which was launched in June last year, Miwatek principal process engineer Sebastian Franzsen told Mining Weekly Online on Wednesday.

Miwatek MD Herman Grobler said traditional AMD processes included up to three stages of pretreatment followed by RO, which then produced a brine that had to be processed, usually through crystallisation.

Miwatek developed a caustic reactor which turned the brine produced in the first stage of RO into a neutralising agent that was then used in the treatment process. The brine was recycled and the process simplified.

The Miwatek process now consisted of pretreatment, RO, and the treatment of the brine through the caustic reactor, with the treated brine then being reused in the RO process, Grobler explained.

“The caustic reactor, which is the centrepiece of the technology, takes the brine stream, reacts it and separates a gypsum-rich stream, and a hydroxide-rich stream which we call the dilute caustic, [which is then used as a neutralising agent],” Franzsen pointed out.

He added that the caustic neutralising agent, when used upstream of the RO, reduced the scaling potential of the membranes significantly.

“[However], caustic [as a neutralising agent] is traditionally a lot more expensive than lime is, therefore, the novelty in the neutralising side is that we are generating caustic from lime and the unconventional aspect of the technology is in the chemical regime we operate,” Franzsen said, adding that the company closed the loop for a zero-liquid discharge process that did not include crystallisation.

He told Mining Weekly Online that while Miwatek had only started with the piloting of this optimised process in January this year, the company started working on the concept more than a year ago. Grobler added that the operation would be easy to scale up for commercial application as it used existing water treatment equipment.

Grobler pointed out that the technology had received a lot of interest from countries such as Peru, Chile and Ghana; however, there had been limited interest from within South Africa.

“In the last year or so, very few tenders of this type have gone out in the [South African] market,” he said.

The Miwatek technology could be applied to water stemming from coal, gold, copper and silver mining as well as water used in industrial processes.