pH buffering capacity of copper-mine tailing amended with a peat-moss and shrimp
wastes compost
Arnaud S. de Coninck, Antoine Karam and Léon-Étienne Parent
Équipe de Recherche en Sols Agricoles et Miniers, Department of soils and agrifood engineering,
2425 rue de l’Agriculture, Pavillon Paul-Comtois, Laval University, Quebec, Canada, G1V 0A6.
The sensitivity of copper-mine tailing amended with peat-moss and shrimp wastes compost to
pH changes is important to know in order to design proper tailing management schemes when
these tailings are cultivated or phytoremediated. The objective of this experiment was to
evaluate the pH buffering capacity (pH BC) of: (i) a Cu-mine tailing (pH 7.70) treated with 3
rates (0, 5 and 20%) of organic amendment and (ii) a calcite mineral collected from the tailing
site. Calcite was coated with the green mineral malachite, Cu2(CO3)(OH)2, as identified by
infra-red spectroscopy and scanning electron microscope coupled with an energy dispersive
analysis of X-ray. The aqueous sorbent suspension was titrated with 0.5 M HCl. Thirty
minutes were chosen as time interval between additions. The sorbent suspension was
continuously stirred during titration and the pH was measured after stirring at the end of each
time interval. The results showed that calcite exhibited much higher buffering capacity than
compost. The titration curve of unamended tailing was characterized by one break point,
similar to that for weak base or aqueous carbonate solution versus strong acid. Up to 0.95
mmol of added H+, the pH BC of sorbents increased in the following order: calcite >
unamended tailing > compost amended tailing > compost. Above 0.95 mmole of H+, the order
was: calcite > compost > unamended and compost amended tailings. The addition of compost
reduced the pH BC of the tailing. Consumption of H+ was linearly increased for compost. The
carbonate buffer system was the major factor controlling the ability of Cu-mine tailing system
to withstand a large change in pH when acid was added. The Cu mine tailing and calcite
mineral appeared to be well buffered against changes in pH, so that acid conditions can hardly
occur.