Manufacturing Brick from Attapulgite Clay at Low Temperature by Geopolymerization

Ground to approximately 250-mesh size powder, attapulgite mining waste was mixed with different alkali concentrations (4, 8 and 12M NaOH) to form thick paste and statically compacted (~10 MPa). The samples were cured at 40 ° C and 60 % RH for long-term storage (1 week–3 months) and at 120 ° C and 0 % RH for short-term storage of varying periods of time (6, 12 and 24 h). This particular clay was characterized using a variety of techniques including physical (DTA, X-ray, laser granulometry, microstructure, PSD, etc.) and chemical analysis. The main minerals present are palygorskite, quartz, calcite and hematite. DTA/TGA curves resemble those obtained when a sample of kaolin is first heated and then cooled. When treated with 12 M-alkali solutions and cured for 7 days at 80 ° C, the minerals present are montmorillonite, larnite, stilbite, dolomite and calcite. Palygorskite clay disappeared after the reaction. In long-term tests, strength did not increase with time for attapulgite clays activated with sodium hydroxide. For all concentrations and periods, the strength obtained with 8 M concentration was greater. In short-term tests, the maximum strength was obtained after 24 h for 12M concentrations. After 12 h of curing, alkali activation of attapulgite at 120 ° C appears to be much more advantageous in terms of strength. The fiber structure of the attapulgite disappeared and was completely changed into one resembling plates. The low conductivity obtained suggests that the Na component of the 8 and 12 M brick reacts nearly completely.