Mining Weekly

Unwanted carbon dioxide (CO₂) produced in industrial processes, which is often too expensive to capture, can effectively be used in the mining industry to treat the problem of acid mine drainage (AMD), using the Council for Scientific and Industrial Research’s (CSIR’s) Alkali Barium Calcium (ABC) desalination process, as opposed to the common lime treatment process.

Sulphur recovery from gypsum processing using CO_{2 is also a good method of capturing unwanted CO2.}

These alternatives were highlighted by Royal HaskoningDHV industrial process portfolio manager David Johnson at the ninth yearly South African Energy Efficiency Convention, held at Emperors Palace in Johannesburg, last month.

Johnson, who helps large industry to optimise their operations, while also seeking energy efficiency opportunities, points out that State-owned power utility Eskom is the largest CO_{2 emitter in South Africa, while miners BHP Billion, Anglo American and Gold Fields, cement producer PCC, as well as petrochemi-cals group Sasol are also emitters of CO2.}

These emitters are currently using coal, which is in high demand and currently facing an industrial-use shortage, to clean their process water, says Johnson.

He instead suggests using the CSIR’s ABC process as an alternative, which can desalinate an estimated 200 M∙/d of AMD.

The ABC process extracts and precipitates the calcium carbonate out of the steam by adding CO_{2 to the reaction process.}

In a plant that is used to desalinate 200 m∙/d of AMD, one can avoid producing 132 t/d of CO_{2 and absorb a further 237.6 t/d.}

This process works similarly in gypsum processing, where a high purity sulphur can be recovered from the process by adding CO₂ to the reaction process.

In the process, the gypsum is reduced to calcium sulphide and the sulphide is stripped using CO_{2 gas to produce the sulphur.}

This process recovers about 600 kilotons of sulphur and 2 750 t of CO_{2 a day.}

By using this process as an alternative to the use of lime as a neutralising agent in AMD, additional CO_{2 can be absorbed, says Johnson.}

In addition, the increasing use of the ABC process over the lime treatment process in the AMD treatment process will also reduce the production of CO_{2 at source in the cement factory, which produces lime from limestone through the burning of coal.}