Microbial and copper adsorption by smectitic clay--an experimental study.

The objective of this study was to quantify copper-, bacteria- and bacteriophage-binding capacities of natural clay with the aim of predicting the adsorption of heavy metals, human pathogenic bacteria and viruses by a clayey landfill liner. X-ray diffraction analysis of six natural clays showed that the dominant phase in all deposits consists of smectites together with illite, kaolin and, sometimes, palygorskite and sepiolite. The specific surface areas of different clay substrates were very high ranging from 293 to 351 m2 g(-1), and indicating a high proportion of phyllosilicates, consisting especially of smectites. The physico-chemical identification of separated smectites showed a high potential adsorbent character indicative of a large industrial use. The Kb12 smectite substrate chosen arbitrarily among six separated substrates, appeared as an excellent copper adsorbent. Copper was adsorbed to clay in a proportion ranging from 94.6 to 96.0% with an average of 95.1% and its adsorption occurred rapidly in less than 30 min. Organic contents of the clay substrate, evaluated as 17% of dry mass, may contribute and enhance copper adsorption. Different elution protocols using distilled water, 2 and/or 5% nitric acid revealed that while nitric acid resulted in the removal of more than 59% of the metal at the lower concentration and its complete depletion with a further elution at the higher concentration, distilled water alone was unable to remove more than 1% of adsorbed copper. This finding suggested that copper ions form high-energy bonds with layer-silicate surfaces. Interestingly, the use of a regenerated substrate as copper adsorbent subsequent to abundant washings of the used substrate consecutively, with 0.1 N HNO3 and distilled water, reduced copper adsorption by approximately 14%, suggesting a slight disturbance of clay initial structure. Batch adsorption experiments with phage T7 and raw clay Kb12 showed that the tested clay substrate appeared as a relatively moderate phage adsorbent since the quantity of adsorbed phage averaged 98.2 +/- 0.88% (2 log10 retention) as measured by infectivity for Escherichia coli ATCC 11303. As shown by two types of separating procedures, natural sedimentation and a low speed centrifugation, bacteriophage particles were bound essentially to fine and not to relatively coarse particles of the clay suspension. The retention capacity of purified clay Kb12 appeared low, with average values lower than 60 and 50%, for Pseudomonas aeruginosa ATCC 15442 and Bacillus cereus ATCC 1135, respectively. A significant increase of retention, in the order of 30%, was found for both bacteria when the mixture clay-bacteria was incubated at laboratory temperature for 6 hours.