A process and apparatus for manufacture of oxide products for use as biocide, chemical detoxifying, and catalytic support products, from caustic calcined carbonate powder, preferably from magnesite, dolomite, or hydromagnesite, is described. These oxide particles are characterized by high surface area, high porosity and a high degree of calcination, and the method of manufacture utilizes an indirectly heated counterflow reactor. The oxides may be used as a powder, granules, or formulated into a slurry and used as a spray, emulsion, foam or fog, or the powder product may be directly applied. Also described is the formation of particles with microstructures defined by at least one nano-crystalline structure positioned on the outer surface of the particles.