Hydraulic Cement Systems for Stabilization/Solidification - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 62

cement. 53 In an early study, masonry cement was also used for solidification of low-
level radioactive wastes. 54

4.3 LIME-POZZOLAN CEMENT

Lime-pozzolan mortars have been used by humans for centuries. 55 These materials
were widely used in the masonry construction of aqueducts, arch bridges, retaining
walls, and buildings during Roman times and have earned a good reputation of
durability. 56 The invention of portland cement in the 19th century resulted in a
reduction in the use of lime-pozzolan cements because portland cement shows a
faster setting time and higher early strength. In the past 50 years, lime-pozzolan
cements have again come under investigation, especially in some developing coun-
tries, because of their low cost. The hydration of lime-pozzolan cements are the
same as those described for portland pozzolan cements.
Lime-pozzolan cements have been successfully used for treatment and delisting
of several hazardous wastes. In one case, 58 lime-fly ash cement was used to treat
electric AFD, which contains hexavalent chromium, lead, and cadmium and is listed
by USEPA as hazardous waste designation K061. TCLP test indicated that contam-
inants in the leachate from treated waste were all brought into compliance with
regulatory criteria. The process, with a trade name of Super Detox Process, as
illustrated in Figure 4.2, entered commercial operation in Illinois in 1989 and had
processed 120,000 tons of electric AFD when reported by Smith. 58
In another case, a steel manufacturer generates about 240 wet tons per year of
filter cake from its chromium wastewater treatment operations. 59 This filter cake is
classified as EPA Hazardous Waste Code F006. The concerns for F006 are cadmium,
hexavalent chromium, nickel, and complexed cyanide. The waste generated contains
chromium (III) produced from the reduction of spent chromium passivation and
plating solutions. The steel manufacturer used a lime-fly ash mixture to adsorb or

Pozzolan
silo

Lime
silo

Feeder
units

Waste

Mixer

Landfill

Stabilized
waste

FIGURE 4.2 Illustration of lime-pozzolan cement stabilization process. 58