Bentonites from Northpatagonia to be used in compacted clay liners

MUSSO, TELMA BELÉN; SILVA, GRACIELA; VALLÉS, JORGE; PETTINARI, GISELA; DI NARDO, LUCIANO; ROEHL, KARL ERNST

Castellaneta Marina, Italia

Congreso; XIV International Clay Conference; 2009

Association Internationale pour l'Etude des Argiles

Two types of Northpatagonic claystones (a commercial sodium bentonite CATAE and a smectite rich claystone DTN2) are considered as potential liner materials and studied in mixtures with sand to evaluate its permeability properties. Both rocks are interbedded in Allen Formation (upper Cretaceous) which represents a littoral sedimentary sequence developed in the eastern part of the Neuquén Basin, Argentina. The aim of this work is to evaluate a new material with low mining cost and to compare it with a commercial bentonite widely used in petroleum and ironand steel foundry industry. To check the suitability of the claystones for use as a liner, some physical and chemical tests were performed. Based on hydraulic conductivity measurementsconducted with mixtures consisting of a poorly graded sand (SP) and 3, 6, 9 and 12% of a commercial bentonite, similar mixtures with 9 and 12% of smectite rich claystone from Northpatagonia were evaluated. Hydraulic conductivity measurements of the powdered clays alone and of the mixtures were carried out through consolidation test and falling head method  (rigid wall permeameters), respectively. The evaluated properties are similar for both materials showing in general higher values for the commercial bentonite: swell index (36 vs 30 ml), liquid limit (340 vs 234%), CEC (104 vs 78 meq/100g) and % smectite (90,5 vs 82,3). Na+ is the main exchangeable cation. Differences in mineralogical composition arise in higher quartz content and presence of illite in clay fraction for DTN2. Hydraulic conductivities of the pure samples are 4,2 x 10-10 cm/s for CATAE and 6,1 x 10-10 cm/s for DTN2. Hydraulic conductivity of the mixtures with 9% of clay fall well below the values stipulated at laboratory level by international regulations for compacted clay liners in municipal waste disposal repositories (CATAE: 2 x 10-9cm/s, DTN2: 6,8 x 10-9 cm/s). In mixtures with this type of sand, both materials meet the requirements for an acceptable waste barrier liner adding just 9% of clay. This percentage could be lower if a soil is used in the mixture instead of sand which is a common practice in landfill  construction. The properties and behaviour of the tested smectite rich claystone DTN2 allow us to classify it as a bentonite. In this way, a new applicability for clay materials of regional  provenance was found.