posted on 2016-02-20, 04:52authored byEmily
P. Rhodes, Zhiyong Ren, David C. Mays
Because
tires contain approximately 1–2% zinc by weight,
zinc leaching is an environmental concern associated with civil engineering
applications of tire crumb rubber. An assessment of zinc leaching
data from 14 studies in the published literature indicates that increasing
zinc leaching is associated with lower pH and longer leaching times,
but the data display a wide range of zinc concentrations, and do not
address the effect of crumb rubber size or the dynamics of zinc leaching
during flow through porous crumb rubber. The present study was undertaken
to investigate the effect of crumb rubber size using the synthetic
precipitation leaching procedure (SPLP), the effect of exposure time
using quiescent batch leaching tests, and the dynamics of zinc leaching
using column tests. Results indicate that zinc leaching from tire
crumb rubber increases with smaller crumb rubber and longer exposure
time. Results from SPLP and quiescent batch leaching tests are interpreted
with a single-parameter leaching model that predicts a constant rate
of zinc leaching up to 96 h. Breakthrough curves from column tests
displayed an initial pulse of elevated zinc concentration (∼3
mg/L) before settling down to a steady-state value (∼0.2 mg/L),
and were modeled with the software package HYDRUS-1D. Washing crumb
rubber reduces this initial pulse but does not change the steady-state
value. No leaching experiment significantly reduced the reservoir
of zinc in the crumb rubber.