Approximately 50,000 tons of sewage sludge are generated in Qatar every year as by-product from the treatment of municipal wastewater. The sewage sludge contains a wide range of contaminants, such as heavy metals, pathogens, and organic pollutants, and its disposal presents significant challenges due to its potential impact on human health and the environment. Thermally dried sludge pellets are only permitted for use in landscaping and their use is declining with time, with the majority sent to landfill. The government is considering the ban of sewage sludge landfilling due to the potential risks of accumulated contaminants. The present technology provides an innovative solution for the conversion of sewage sludge into cementitious material for use in the construction industry.

A method for converting a starting material containing at least 40 wt.-% of calcium silicon (hydr)oxide phases and calcium aluminum (hydr)oxide phases into an SiO2 rich SCM and a calcium carbonate additive includes the steps: providing the starting material with a D.sub.90 of 1 mm, mixing the starting material with water or adjusting the water content to provide a starting material slurry having a solid:liquid weight ratio from 2:1 to 1:100, passing the starting material slurry together with carbon dioxide into a gravity separation reactor, subjecting the starting material slurry and carbon dioxide to centrifugal motion inside the reactor, and removing a heavy slurry from a first outlet of the reactor, removing a light slurry of lower density particles from a second outlet of the reactor, and removing liquid at a third outlet of the reactor.

Disclosed is a combined process of integrating stopping-backfilling and carbon storage. The combined process includes the following steps of: determining a cyclic interval of a working face through measured data of a mine pressure of a fully-mechanized coal winning working face; when the stopping distance of the fully-mechanized coal winning working face reaches a backfilling isolation interval, providing a backfilling tarpaulin behind a hydraulic support, and pumping, through a backfilling pipeline, backfilling slurry to a backfilling area along a support beam; when the area is backfilled with the backfilling slurry, injecting supercritical carbon dioxide into the backfilling slurry; and allowing the supercritical carbon dioxide to fully react with the backfilling slurry to solidify the backfilling slurry.