THE EFFECT OF HEATING AND QUENCHING ON GRINDING CHARACTERISTICS OF QUARTZITE

The effect of heating quartzite from room temperature to 650 degrees C in 1 h then quenching in various aqueous media has been investigated by two different methods. Operating work index tests were used to dete rmine the effect of this process on the grinding energy required for s ize reduction of the material over an hour of milling. Ultra-fast load cell (UFLC) tests were carried out to determine the effect of the pro cess on the specific fracture energy E and the particle strength sigma (p) of the material prior to milling. The UFLC tests showed that the a queous media quenches caused a significant reduction in both E and sig ma(p), compared with the untreated material; acid, alkali and salt sol ution quenches caused further reductions in these values compared with water-only quenching. The operating work index tests showed that aque ous quenching reduced the grinding energy required for the first 30 mi n of milling, and this effect was still noticeable after 60 min of mil ling in the case of acid, alkali and salt solution quenches. The two i ndependent test procedures have established the effectiveness of this process for weakening quartzite. (C) 1998 Elsevier Science S.A.