The extraction and processing of marbles, rocks and granites produces a significant
amount of waste materials, in the form of shapeless blocks, scraps, gravel and sludge.
Current regulations and a greater concern to the environment promote the reuse
of these wastes: quartz-feldspathic materials are successfully used for ceramics,
crushed porphyry as track ballast, whereas carbonatic wastes for lime, cement and
fillers. However, there are currently no reuses for serpentinitic materials: a striking
example is represented by the Valmalenco area (central Alps, northern Italy), a
relatively small productive district. In this area 22 different enterprises operate in the
quarrying and/or processing of serpentinites with various textures, schistose to
massive, and color shades; the commercial products are used all over the world and are
known with many commercial names. The total volume extracted in the quarries is
estimated around 68000 m3/yr. and the resulting commercial blocks and products
can be estimated around the 40 - 50 % of the extracted material. The processing
wastes can vary significantly according to the finished product: 35 % of waste can be
estimated in the case of slab production, whereas 50 % can be estimated in the
case of gang-saw cutting of massive serpentinite blocks. The total estimate of the
processing rock waste in the Valmalenco area is about 12700 m3/yr; together with the
quarry waste, the total amount of waste produced in the area is more than 43000
m3/yr. The sludge (approximately 12000 m3/yr, more than 95 % has grain size <
50 micron) mainly derives from the cutting (by diamond disk and gang-saw) and
polishing of massive serpentinites; it is filter-pressed before disposal (water content
ranging from 11.5 to 19.4 wt. %). All the different waste materials (85 samples) were
characterized by quantitative XRPD (FULLPAT software), whole-rock geochemistry
(ICP-AES, ICP-MS and Leco®) and SEM-EDS. The mineralogical composition is
quite variable from quarry to quarry, with abundant antigorite (up to 90 wt. %) and
olivine (up to 38 wt. %), and variable contents of diopside, chlorite, magnetite,
chromite and brucite. The chemical composition reflects the protolith: MgO 35.1 –
42.7 wt. %, SiO2 38.8 – 42.3 wt. %, Fe2O3 7.1 – 8.8 wt. %, Al2O3 0.9 – 2.8 wt.
%, CaO 0.2 – 3.1 wt. %, Cr2O3 0.26 – 0.35 wt. %, Ni 1800 – 2100 ppm; little
differences can be observed in trace elements. SEM-EDS investigations evidenced little
amounts of chrysotile asbestos fibers (generally < 1000 ppm, mean values 200 –
400 ppm), deriving from cracks, fissures and veins of the waste blocks. Very few
published studies on the reuse of serpentinitic wastes can be found. Finely ground
antigorite-rich materials could be used as filler for plastics (instead of talc), whereas
olivine-rich wastes as a reactive fixing carbon dioxide (as carbonates) released
during the use of fossil fuels. In the ceramic industry, the most promising target is
represented by forsterite and/or high-MgO ceramics and forsterite refractories (with
periclase addition), but also by cordierite ceramics (adding kaolin) and high-hardness
vitroceramics. The real possibility of an industrial use of serpentinitic materials will
require much more experimental work, because no relevant previous studies are
available. Special care must be taken to avoid chrysotile asbestos contamination. |