Integration of a wet processing plant into the existing production process of a natural stone plant to increase resource efficiency (Germany)

Challenge the practice is addressing: The quartzite extracted from the "Düro Quarry" is mainly porcessed into high-quality chippings and crushed sands as aggregates for asphalt and concrete, railway ballast, hydraulic construction stones and base course mixtures for road construction. Despite the use of modern plant technology, mineral processing generates co-products such as pre-screened material and simple filler-rich crushed sands, which do not meet quality standards and therefore difficult to market. Up to 15% of the total production has to be landfilled due to a lack of marketability or is used for the simplest applications without quality requirements. Apart from an irregular and fluctuating grain structure, the proportion of fines is the major problem.

Concrete practice to achieve the expected goal: To ensure flexible feeding with different materials, several feeding options were implemented for the wet processing. The pre-screen material generated in the ongoing production process is automatically fed to the wet processing system via belt conveyors. By-products from the secondary crushing plant and from old stock are fed via two fee hoppers for dump trucks and one feed hopper for wheel loaders. Washing and dewatering screening machines in combination with hydrocyclones are used to wash out the fines from the feed materials. Screening into different grain classes also takes place. The washing water from the process is clarified by sedimentation and fed back into the washing process in a circuit. The sedimented fine fraction is fed as homogenised sludge to a chamber filter press, dewatered and discharged as filter cake (by definition clay) that can be marketed to the ceramic industry. The process water and the sludge are conveyed by a system of frequency-controlled pumps, which is monitored by measurement and control technology. Controlling the wet processing plant is done via a PLC with process visualisation, which in turn is connected to the plant's central control system and monitored from the central control room. The entire plant can be operated automatically.

Expected impact/goal of the practice: The aim of the company was to process the co-products of mineral processing into marketable products in order to increase resource efficiency. Within three years, wet processing has increased resource efficiency to 99%. Almost the entire quarry volume can be processed into high-quality construction and aggregate materials and marketed accordingly, including the filter-cake produced in wet processing. Furthermore, large quantities of the existing dumps have been processed in the wet processing plant. The increase of resource efficiency led directly to a reduction in the annual production volume and subsequently to a significant reduction in the consumption of explosives, diesel and electricity, as well as to a reduction in a variety of impacts such as noise, dust, exhaust and CO2 emissions.

Who is the target user group of the practice/intervention or implementing the practice/intervention? This practice is for companies in the extractive industry.