Solidification/stabilization of stainless steel pickling residue with aluminum potassium sulfate amended fly ash.

This article presents an original study on the feasibility of reuse fly ash (FA) solidified/stabilized stainless steel pickling residue (SSPR). SSPR was characterized using different leaching procedure and solidified/stabilized using aluminum potassium sulfate dodecahydrate (KAl(SO 4) 2 .12H 2 O) amended fly ash. A modified four-step Community Bureau of Reference (BCR) sequential leaching test and risk assessment code (RAC) was employed to evaluate the potential hazards of metals in SSPR. Results show that SSPR mainly consists of sulfates and heavy metals. The major elements are Ca and Fe, with the total amount of 191,600 and 122,400 mg/kg. Cr is the most notable metal with a total amount of 22,500 mg/kg. Its concentrations in HJ/T 299 and HJ/T 300 extracts are 28.6 and 285 mg/L respectively. Another metal that is of some concern is Ni, its concentration in HJ/T 300 extract is 229 mg/L and total content in the residues is 10,690 mg/kg. The RAC of four list heavy metals are: Ni (61.36%) > Zn (43.48%) > Cr (20.64%) > Cu (19.83%). Therefore, SSPR has a higher potential to be hazardous to the environment. After treatment by 10% of KAl(SO 4) 2 .12H 2 O with 40% of FA 2 (10KA40FA 2), the concentration of Cr is 7.9 mg/L in HJ/T 299 extract and 12.68 mg/L in HJ/T 300 extract. While these two values for Ni is 0 and 14.34 mg/L. The RAC of the metals after treatment by 10KA40FA 2 followed the order of Ni (20.38%) > Zn (10.59%) > Cu (8.54%) > Cr (7.71%). The unconfined compression strength (UCS) tests showed that the 7-d UCS of the 10KA40FA 2 remolded sample achieved 3556.2 kPa which was much higher than that of raw SSPR remolded sample of 1746.7 kPa. Image 1 • Stainless steel pickling residue (SSPR) was characterized using different extraction methods. • Results indicate that Cr and Ni are the most toxic heavy metals in SSPR. • KAl(SO 4) 2 .12H 2 O amended fly ash can stabilize the heavy metals in SSPR effectively. • The stabilized SSPR has the highest 7-d UCS of 3556.2 kPa. • The SSPR treated by 10% of KAl(SO 4) 2 .12H 2 O with 40% of FA 2 can be safely used as roadbed materials. [ABSTRACT FROM AUTHOR]