Leaching of lead from clinoptilolite at acidic conditions

The leachability of Pb2+ from natural greek clinoptilolite was investigated according to the
standard procedures TCLP/EPA/RCRA (1311), EPA Methods 1310, 1320 and DIN 38414-S4.
Through SEM/EDAX analysis it was shown that lead was uniformly loaded onto the particles
subjected to acid treatment. Sorption was fast during the first few hours and equilibrium was
practically attained after 24 h. pH was the dominant factor affecting leaching and for values 3
and higher less than 1% of the metal was leached out while at pH=1 up to 20% of the lead
initially present on the solid was leached out. At 1.5 and 2, lead was re-adsorbed after initial
leaching. % leaching after 24h was found to increase with increasing initial load (17 to 44%
for 15 to100 mgPb2+/gclin). Agitation rate (50-180 rpm) and particle size (1.4-2 mm and 5-6
mm) did not affect leaching. Higher temperature (25-40 oC) resulted in increased leaching
rates. Despite the limited number of data, leaching seems to follow third-order kinetics.
Finally, exposure to acid conditions increased markedly the specific surface (from 35.1 to 79.4
m2 g-1) and lowered the average pore diameter (from 80.8 to 42.9 Å) of the clinoptilolite
particles.