In Heading to PERUMIN, the Calidra Peru company presented the benefits of lime in water treatment to combat the presence of acid waste and heavy metals.
Juan Cornejo, Calidra Peru's technical commercial advisor, stated that in open pit and underground mines there is always acid drainage, which is formed by three chemical reactions: pyrite oxidation, bacterial action and acid generation. This type of drainage, he stressed, is combated with the application of lime.
"These acid waters are treated using various solutions, such as, for example, alkali treatment, which consists of increasing the pH to promote the precipitation of metals. This type of treatment uses a wide range of products such as caustic soda and calcium hydroxide. The most widely used product is calcium hydroxide, due to its low cost, high availability and its coagulant/flocculant properties", he said.
He added that in water treatment it is important to control the electrical potential. For this reason, he recalled that, apart from raising the pH, lime also tends to slightly reduce the electrical potential. He also emphasized that the amount of lime to be used for acid water treatment will depend on the amount of ions or metallic charge that the liquid contains. "The more ions, the more lime must be used," he said.
In relation to the acid water treatment process, the Calidra Peru representative said that it is important to control the sulfur level and the water temperature, as well as the reactivity and granulometry of the lime, in order to mix both components and obtain the corresponding slurry, which will then be poured into the acid drainage.
"In the case of drainage, we must verify the flow rate, the metal content and that it complies with a pH of less than 6. It will be done through a laboratory test. This is where the slurry and the acid drainage will come together," he said.
He added that, after a time and due to the reactions of the mixture, the result will be a colloidal substance that will require coagulating and flocculating agents for the subsequent separation of the solid and liquid phases (sludge and water).
Juan Cornejo, Calidra Peru's technical commercial advisor, on another occasion stressed that effective water treatment will depend on the correct choice of lime. In this sense, he recommended that this product must comply with an availability of calcium oxide (CaO) greater than 80%, a reactivity greater than 15° C, and that the calcination losses (PPC) of crude oil must be in a range of 1% to 3%.
He also suggested reviewing the quality of the raw material used to make lime. This product, according to Jorge Cornejo, must comply with a calcium carbonate (CaCO3) higher than 92%.
Finally, he indicated that high lime slurry is identified by its low water solubility, presentation of small particles in suspension and a homogeneous distribution. While a similar one of low quality contains large particles (lumps) and sedimentation.