A Comparison between a Stationary and a Semi-Mobile Plant for Wet Processing of Crushed Stone

Crushed stone is the most important type of mineral resource in the Republic of Croatia and is mined in more than 350 exploitation fields. Crushed stone is most often used as aggregate for the production of concrete and asphalt, for which it must satisfy high standards, and thus it is necessary to process it. The wet processing technology in semi-mobile plants, which is increasingly frequent in Europe, has thus far not been used in the Republic of Croatia. This paper provides a comparison of the wet processing technology on an older, stationary and a newer, semi-mobile processing plant in the “Oršulica kosa” exploitation field. It also describes the process of waste washwater treatment and the newer high-pressure pre-washing chamber technology. The costs of extracting stone from a stone massif are the same in both cases ; therefore, in comparing the two plants, the effect of the cost of transportation and stone processing was also taken into account. An analysis of the cheapest possible transportation showed that for a stationary plant, located at a distance of 1950 m from the active worksite, the cost of transport was 4.01 kunas per tonne, or 1.7 million kunas per annum, while in the case of a semi-mobile plant this cost was non-existent. As for processing, it appears that the electric energy consumption of a stationary plant is three times greater than that of a new semi-mobile plant, which amounts to a difference of 0.85 million kunas per annum. As for water consumption, it appears that the water consumption of an old stationary plant is approximately ten times greater than that of a new semi-mobile plant, which amounts to a difference of 0.23 million kunas per annum. Taking into account the potential savings of around 2.1 million kunas per annum, the return of the total investment in a new semi-mobile plant should be realized in the relatively short period of 3.5 years. Beside the economic benefit, we should also emphasize the smaller environmental footprint of the new plant, which is evident in the decreased need for adding fresh water to the process, as well as the significantly decreased need for occupying space with settling basins, seeing as the new semi-mobile plant, as opposed to the old stationary one, purifies and recycles wastewater.