Production of silica and calcium carbonate particles from silicate minerals for ink jet paper coating and filler purposes

In this work, the possibility to produce silica and calcium carbonate particles of nanoscopic scale is studied. The work focuses on processes that can use magnesium- and calcium silicate minerals, such as serpentine, olivine and wollastonite, as raw materials. Experimental research has been initiated studying two different main routes: one using pressurised CO2 as a solvent and another one using strongly acidic solvents. The developed material is to be used as the top coating layer of high quality inkjet papers for high speed printing. The technical concept is to replace the expensive, relatively thick top coating layer of multiple coated premium inkjet paper with a thin top coating of nano silica particles applied directly onto the paper printing surface using either a foam or curtain coating technique. Although our ongoing experimental work has shown that wollastonite can be partially carbonated already at 10 bar total pressure, strongly acidic solvents seem far more favourable for mobilising the silica and allowing the production of pure materials. So far, our experiments have yielded >99 % pure calcite and vaterite particles with crystal sizes in the range of 50 nm to 5 ?m. Pure amorphous silica particles have also been produced with diameters in the range of tens of micrometers, but more work is required to reduce the particle size.