CHEMICALLY BONDED CEMENTS FROM BOILER ASH AND SLUDGE WASTES. PHASE I REPORT AUGUST 1997 - JULY 1998

SUGAMA,T. ; YAGER,K.A.

Brookhaven National Laboratory

关键词: Hardening;    Leaching;    Boilers;    Materials Testing;    Sludges;   

DOI  :  10.2172/801416
RP-ID  :  BNL--69319
RP-ID  :  AC02-98CH10886
RP-ID  :  801416

美国|英语

来源: UNT Digital Library

【 摘 要 】

In exploring methods to recycle boiler ash (BA) and waste water treatment sludge (WWTS), by-products generated from Keyspan's power plants, into commercially viable materials, we synthesized chemically bonded cements (CBC) offering the following three specific characteristics; (1) immobilization of hazardous heavy metals, such as Pb, Ni, and V, (2) rapid hardening and setting properties, and (3) development of high mechanical strength. The CBCs were prepared through an acid-base reaction between these by-products acting as the solid base reactants and the sodium polyphosphate solution as the cement-forming acid reactant, followed by a hydrating reaction. Furthermore, two additives, the calcium aluminate cements (CAC) and the calcium silicate cements (CSC) were incorporated into the CBC systems to improve their properties. Using a CBC formulation consisting of 53.8 wt% WWTS, 23.1 wt% CSC, and 23.1 wt% [40 wt% -(-NaPO{sub 3}-)-{sub n}]{sub 2} the Toxicity Characteristics Leaching Procedure (TCLP) tests showed that the concentrations of Pb, Ni, and V metals leached out from the specimens were minimal. This formulation originally contained {approx} 28800 mg/kg of Pb, {approx} 6300 mg/kg of Ni, and {approx} 11130 mg/kg of V; the amounts leaching into the acid extraction fluid were only 0.15 mg/L of Pb, 0.15 mg/L of Ni, and 4.63 mgiL of V. On the other hand, CBC specimens derived from a formulation consisting of 42 wt% BA, 18 wt% CAC and 40 wt% [40 wt% -(-NaPO{sub 3}-)-{sub n}] displayed an excellent compressive strength of 10.8 MPa at an early curing age of 2 hours after mixing at room temperature. The reason for its rapid hardening was due to a high exothermic energy evolved by the acid-base reaction. Furthermore, when these specimens were immersed for 28 days in water at 25 C, and exposed for 20 hours to steam at 80 C, a very high compressive strength of 3.32 MPa developed. Two physico-chemical factors played an important role in improving the mechanical strength of the specimens: One was the formation of two well-crystallized phases, hydroxyapatite [Ca{sub 5}(PO{sub 4}){sub 3}(OH)] and sodium vanadium sulfate hydrate [Na{sub 2}V(SO{sub 4}){sub 2},4H{sub 2}O], as the reaction products in the cement bodies; the other factor reflected the dense microstructure developed by the growth of these crystalline reaction products. Accordingly, the CBCs derived from these by-products have a high potential for use as remediating material for hazardous heavy metal-contaminated soils, as rapid-setting repair patching and filling materials for damaged roadways and bridge decks, and also as binders in precast concrete products, such as blocks, slabs, and pipes.