The susceptibility to sludging of sulfate and oxide CCA
B T Mutandadzi, P D Evans
Radiata pine sapwood was treated separately with a sulphate CCA-C and an oxide CCA in a pilot scale pressure plant using a full cell process. CCA solutions were recovered from the final vacuum phase, placed in plastic tubes, and their susceptibility to sludging determined by examining changes in solution pH, time required for sludge to form and weight and chemical composition of sludge formed. Sulphate CCA-C solutions showed a pH rise of 0.33 above the initial solution pH of 2.01 and a sludge, largely composed of arsenic and chrome, formed after 6-8 weeks. Oxide CCA solutions in contrast showed smaller pH changes and did not form sludge. Addition of glucose or ethanol to freshly prepared sulphate CCA-C and oxide CCA solutions at 25°C resulted in sludge formation with both formulations but sludge formed earlier and in greater quantities with the sulphate CCA-C. The results indicate that the oxide CCA is more resistant to sludging than the conventional sulphate CCA and suggest that the use of the former in treatment plants could reduce sludge formation. Further methods to minimize sludge formation in treatment plants are also discussed.
Keywords: CCA-C; CCA OXIDE ; FULL CELL PROCESS; SLUDGE FORMATION; CHROMIUM; PINUS RADIATA; IMPREGNATION; pH