Abstract:
This research study investigated variation in chemical compositions of the solidified wastes at different hydration times. The
synthetic rice husk ash (sRHA) was used to replace for ordinary Portland cement (OPC) at 0%, 10%, 20%, 30% by wt. and to
combine with hydrated lime at the weight ratio of 55:45. Sodium silicate and sodium carbonate were used to activate the hydration
reaction of lime and sRHA at 8% by wt. The synthetic zinc hydroxide and the plating sludge were added to the cement mixes
at 10% by wt. Water to solid ratios (W/S) of 10 and 20 were used for OPC/sRHA/Heavy metal and Lime/sRHA/Heavy metal
mixes. Solution chemistry data shows that pH of filtrates separated from OPC slurries increased from 12.35 to 12.66 during hy
dration time of 3 days. When the plating sludge and the synthetic zinc hydroxide were added, pH of the filtrates decreased from
12.23 and 12.21 to 12.04 and 11.96, respectively during the first hour of hydration and increased to 12.63 and 12.54 thereafter.
Concentration of OH- ion varied in a similar manner to that of pH. A gradual decrease in concentration of sulfate and calcium
from 1,493 and 1,282 to 335 and 721 mg/L, respectively were observed throughout the designated hydration time.
For lime/sRHA mixes, concentration of Si in the filtrates containing sodium silicate was 189 mg/L during the first minute of
hydration and decreased to 1.3 mg/L within 3 days. When sodium silicate was not added to the cement mixes, concentration
of Si remained lower than 0.251 mg/L throughout the experiment. In addition, a considerable lower Zn concentration in the
filtrates separated from the samples containing sodium silicate was found.