Silicon release and its speciation distribution in the surficial sediments of the Pearl River Estuary, China

Liberation experiments have been undertaken to explore silicon release from the surficial sediments of the Pearl River Estuary, China. Three environmental factors are selected including agitation time, pH value, and salinity. Results show that a logarithmic relationship between dissolved silicon concentration and time is observed. After the initial rapid release, a dynamic balance is accessed for 14 h and the maximum release is 46 μg g−1. There is a decrease trend of silicon release with increasing pH value. The silicon release decreases rapidly from 50 to 42 μg g−1 as pH value increases from 3 to 5, whereas from pH 5 to 9, the decrease trend is mild from 42.5 to 40.3 μg g−1. Silicon release is intimately related to seawater salinity, illustrating a significant correlation (r = −0.995, p = 0.01). Liberated silicon is 21.18–22.76 μg g−1 at the salinity of 35, reducing by 43.5–44.5% compared to those leached with de-ionized water. Silicon speciation analyses are performed to both the initial and the liberated sediments based on a sequential extraction procedure. The exchangeable fractions in the initial and liberated sediments average 18.89 and 13.6 μg g−1, respectively. This result suggests that silicon liberation with de-ionized water does not exert a prevailing influence on the subsequent exchangeable extraction.