A switch from ball mills to Vertimill® boosts Miaogou Iron Mine’s transformation

The Miaogou Iron Mine, part of the Hebei Iron and Steel Group, is located in China’s Qinglong County, some 300 kilometers east of Beijing. Its annual iron concentrate production is 800,000 tons.

Due to the recent downturn in the iron and steel industry, Miaogou’s concentration costs were exceeding the price of iron concentrate. This put significant pressure on the company’s operations. Something had to be done.

Improved recovery, less energy

The mine’s original grinding circuit consisted of ball mills exclusively. The primary stage comprised 5 ball mills, the secondary stage 3 ball mills, and the final, tertiary stage 2 ball mills. The original tertiary grinding fineness was -325 mesh with 71-73% passing. Iron concentrate grade was 65% and the average recovery rate 87%.

Since the technological transformation, the concentration costs have basically paralleled the current price of iron concentrate. Under the current market situation, the normal production of the mine can still be guaranteed. Through the introduction of Metso’s Vertimill^® VTM1500 vertical grinding mill, Miaogou Iron Mine has not only successfully achieved the goal of the technological transformation, it has also laid the foundation for smoothly riding out the current market's difficulties.

“After replacing the original tertiary ball mills with a Vertimill VTM1500, the grinding fineness was increased from 71-73% to 88-90% passing -325 mesh, the iron concentrate grade from 65% to 66%, and the average recovery from 87% to 89%. At the same time, the silica content was decreased by 1%,” says Zhang Runshen, General Chief of Miaogou Iron Mine Project and Chief of Concentration Plant.

In addition to having helped improve the recovery rate, the Vertimill has a lower energy and grinding media consumption rate than the ball mill. It also takes up much less space.

“We would have needed a larger ball mill to achieve the current grinding fineness. However, the original plant space was limited. Thanks to its compact dimensions and the ease of installation, it only took us two weeks to complete the equipment installation. At present, the VTM1500 runs at an 85% load to achieve a capacity of 200 tons per day. Eliminating the original two ball mills that had a high rate of energy consumption has resulted in an energy savings of 30%,” says Zhang Jiankang, Grinding Plant Technician at the Miaogou Iron Mine.

The Vertimill VTM1500 also has a significantly lower grinding media consumption. The media consumption of processing the raw ore dropped from 0.8 kg/t to 0.3 kg/t, equivalent to a 60% reduction. With an annual output of 800,000 tons of iron concentrate, the savings in grinding media alone can amount to RMB 2.4 million Yuan per year.

98% availability

After more than 7 months in operation, Metso’s field service engineers along with the customer carried out an inspection of the Vertimill. The wear pattern of the end liner was good and should allow at least 3 more months of use. Thanks to the extremely long wear life of Metso’s screw liners, the mill’s availability reaches 98% and everyday maintenance costs are reduced.

“Metso possesses a high-efficiency automation system, and the mill can be managed by a single operator now. In addition, unlike the noisy ball mills, the VTM1500 operates much quieter,” says Zhang Jiankang.

“Metso’s VTM1500 has demonstrated very obvious advantages in terms of energy consumption reduction, labor saving and working environment improvement.”