Local supplier of limestone and subsidiary of agricultural limestone manufacturer PBD Boeredienste PBD-Lime reports it is diversifying and improving its product and service offerings to supply niche markets.

PBD-Lime GM Siegfried Schubert says the limestone industry is not a very significant industry in South Africa and PBD-Lime had to diversify its business units to be more competitive locally and overcome challenges facing the industry.

The company has invested over R10- million since 2009 to improve the processes and management of its INCA-Mining lime- stone processing plant, in the Immerpan area, which is located 40 km south-east of Mokopane, in Limpopo province. The investment resulted in reduced unit costs and increased productivity.

The company will invest a further R8-million in improvements at the operation, during the next financial year. The INCA-Mining operation still has thee-million tons of limestone in excess to be mined for specialised purposes, such as glass manufacturing and ferrochrome smelters, over the next 10 to 15 years. However, the operation can still produce limestone for agricultural purposes such as fertiliser filler material and animal feed for the next 20 years, he says.

Acid Mine Drainage
Further, the company is shifting its focus to acid mine drainage solutions for South African mines.

Schubert says limestone can be used to treat acidic water in a two-step process.

Generally, only expensive calcium hydroxide, or slaked lime, which is an inorganic compound with the chemical formula Ca(OH)2, is used to neutralise acid water and extract heavy metals.

Schubert explains the first step of the two-phase process is to add the limestone to the acidic water to increase its pH level.

The second step is to add the calcium hydrox- ide, which binds with heavy metals in the water. The heavy metals can only bind with the calcium hydroxide if the pH level is high enough; therefore, it is important to first raise the pH level.

The amount of calcium hydroxide needed in the second step is significantly lowered, as the water has been prepared to optimally increase the reaction of heavy metals with calcium hydroxide.

The two-phase process results in cost savings as less of the more expensive calcium hydroxide is needed. The cost of limestone is on average about a tenth of the cost of slaked or unslaked lime. Mines wanting to use the two-phase process have to buy 1.6 to 2 times more limestone than lime to get the job done, as the limestone has a lower neutralising capacity; however, a cost saving of between 60% and 75% is still possible, even if nearly double the amount of limestone is needed.

In addition, limestone with a lower neutralising capacity, such as that mined by PBD- Lime, should be used in the first step, ultimately, resulting in cost savings for the mines, as they do not have to buy high-quality lime. This also eliminates the need to transport the limestone from the Northern Cape region, where high-purity calcium carbonate sources are situated.

Schubert says a contributing factor, which makes these savings possible, is the central location of PBD-Lime’s quarries in areas such as Middelburg, Mokopane, Meyerton and Orkney. “The location of our quarries enables us to deliver limestone at a lower overall cost owing to reduced logistics, which resulted from the establishment of the company’s own logistics fleet of 30 side-tipper link trucks, among others,” he adds.

Mining Rehabilitation
Further, the company is investigating the poten- tial for developing customised mine rehabilitation solutions. The company has entered into discussions with the University of Pretoria’s Faculty of Natural and Agricultural Sciences to help develop long-term soil rehabilitation solutions using limestone.

Currently, mines are using ultrafine lime mixtures to neutralise excavations that have been filled with acidic soil. The advantage of the ultrafine lime is that it reacts instantly, as it is highly dissolvable. The disadvantage is that it does not penetrate and seep through to the deepest layers of the soil, leaving the areas where plants take root acidic and hostile, resulting in soil that is unsuitable for agricultural use.

The solution PBD-Lime proposes entails limestone, varying in size and dissolvability, to be buried in the soil at various depths. The size and dissolvability of the product will ensure continuous release of neutralising minerals into the soil, resulting in a long-term solution for the neutralisation of acidic soil.

Schubert notes that similar techniques are being used in the US to rehabilitate excavated soil. “In some cases, entire wetlands are successfully created as part of passive systems, using limestone to neutralise and filter acid soil and water,” he says.

The mining soil rehabilitation solutions will be tested during the next year, and the first results are expected to be available in the next two months.

Expansions and Improvements of Operations
Meanwhile, the company is investigating the viability of opening two new mining operations in the North West province as part of its long-term planning.

Schubert says the company has successful dolomite and calcite operations in other provinces, and now it wants to tap into the calcite market in the North West to enable the company to compete with other industry players in the area.

The company has identified calcite sources in the province and is in the process of either acquiring mining rights or establishing a partnership with the current owner of the resource.

PBD-Lime has made an offer on a second calcite mining operation, and will acquire the prospecting rights once it has been established whether a significant amount of calcite is available at the operation.

Further, the limestone producer is investigating the viability of constructing two air classification plants to produce ultrafine limestone for industries such as water treatment.

Schubert explains the plants will either be constructed at the company’s INCA-Mining operation or the Calmasil limestone process- ing plant, in Middelburg, Mpumalanga. “We will initially construct a demonstration plant to establish if the operation will be economically successful; thereafter, we expect full operations to start in February, next year,” he adds.

Meanwhile, the company has installed a rotary dryer at its INCA-Mining operation to reduce the moisture content of the fertiliser filler to below 2%. Schubert says this enables the company to supply filler throughout the year. “Most other suppliers can only produce filler during the dry season, whereas INCA-Mining can produce filler the whole year round,” he says.

A coating system will also be installed at the operation during this month. The coating will reduce dust generation in the offloading and packaging processes.