Improvement of desulfurization performances of waste cement particles by acid treatment

We studied the effect of acid treatments on the desulfurization rate of waste cement, a byproduct in the recycling of aggregates from waste concrete. Calcium components in the waste cement were partially extracted by treatment with carbonic acid (aqueous solution of high-pressure CO2), hydrochloric acid, or acetic acid. The desulfurization rate was examined using a thermogravimetric method. The desulfurization rates in the initial stage of the reaction (<5 min) were almost unaffected by the treatments with acetic acid and hydrochloric acid, provided the degree of calcium extraction was lower than about 30%. However, the desulfurization rates at a later stage were lower than that of the original waste cement. The desulfurization rates of the waste cement treated with carbonic acid were higher than those of the original sample for all reaction times studied when the degree of calcium extraction was in the range of 4.13-8.54%. The desulfurization rate normalized by the amount of calcium remaining in the waste cement was higher for all samples with acid treatment than for the original sample when the degree of calcium extraction was lower than 60%. The desulfurization rates of the acid-treated waste cements were significantly higher than that of limestone, a conventional sorbent used in dry desulfurization.