Leachable Characteristics of Arsenical Borogypsum Wastes and Their Potential Use in Cement Production

In this study; the potential use of arsenical borogypsum wastes (ABW) as a set retarder in cement industry was investigated. The comparative performances of arsenical borogypsum wastes (ABW) and natural gypsum samples (NG1 and NG2) at different proportions in the range of 3-8 wt % were tested based on compressive strength over 1, 2, 7, and 28 days and setting times. The use of ABW was observed to lead to a somewhat slower rate of development of strength of the mortar samples than those of NG1 and NG2 during the curing period of 7 days. This is the indication of the effectiveness of ABW as a set retarder. The 28-day compressive strength of mortars tended to decrease with the addition or increasing the proportion of ABW, beyond 5 wt % in particular The data for setting times of the cement products confirmed set retarding characteristics of ABW with an initial setting time of 90-120 min at 3-5 wt % dosage, which conforms to the desired setting time of >= 60 min for CEM I (42.5 N) type cement ITS EN 197-1). Leachability tests (TCLP and SPLP) have also shown that ABW can be classified as a nonhazardous waste; but it can readily release metals such as As and Mn, in particular, whereas the mortar samples containing ABW-cement clinker present no environmental concern with its remarkably reduced leachability.