Two Wirtgen Surface Miner 2200 SMs are helping to produce enormous amounts of ‘white gold’ in the world's largest salt fields located close to Guerrero Negro in Mexico’s west.
Exportadora del Sal (ESSA), a joint venture between the Mexican government and Mitsubishi Corporation, has produced salt on a large scale in the Ojo de Liebre Lagoon since 1957. With a total area of 33,000 hectares, this gigantic evaporation pond is now the largest salt works of its kind.
The salt layer grows by around 20cm every year and must be removed with utmost precision to ensure maximum exploitation of the material and create a clean, level surface to optimise the formation of a new crust.
In order to extract the material, an area of about 250 square kilometres was subdivided into ponds measuring 400m square, into which sea water is drawn. The wastes produced during the evaporation process are discharged into an adjacent field.
In the past, the salt in the ponds was extracted by graders and dozers, but the hard crust on the adjacent field was too hard to be mined so the field remained fallow. However, as global demand for the so-called ‘waste product’, which is used as industrial salt particularly in the chemical industry, continued to rise steadily, ESSA looked around for a suitable mining solution.
Surface mining technology emerged as an option following consultations with applications technology specialists from Wirtgen, taking into account the characteristics of the heavy equipment, the geological conditions of the region, sedimentation and local logistics.
The Wirtgen Surface Miner 2200 SM was chosen due to its 708kW/963PS engine, maximum cutting depth of 25cm and working width of 3.8m. The cutting drum is mounted near the machine’s centre of gravity, ensuring optimum cutting performance and a level, stable surface.
In the field, Wirtgen says the surface miner reliably extracted the extremely hard waste product in exactly the required granulation and minimised the proportion of fines by mining selectively. What’s more, the surface produced by the innovative automatic levelling system LEVEL PRO in combination with laser sensors was absolutely plane.
ESSA consequently decided to use a second 2200 SM to extract the high-quality salt in the main pond, which is mainly produced for the food-processing industry. Here too, the salt around the edges is considerably harder than in the middle of the pond. In addition, the entire area is studded with hard ‘islands’ which, not uncommonly, display a hardness of up to 25MPa.
A uniform surface is vital, particularly for guiding the water drawn into the pond. Together with the lower fines content that is lost in washing when the salt is processed, these criteria have a major impact on the quality of the product. ESSA had determined to improve both the quality and productivity through its mining methods.
Practical experience soon showed that the machine operated optimally at an average cutting depth of 20cm at a working speed of 15 to 20 metres per minute.
The 2200 SM produces up to 1,300 tonnes of salt per hour on average, with a fuel consumption of just 0.12 l/t. As a result, the customer has boosted its annual output to 8 million tonnes and is planning a further increase to 10 million tonnes per year in the future.
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