Effects of iron precipitation and organic amendments on porosity and penetrability in sulphide mine tailings

This paper evaluates the effects of organic amendments and iron precipitation on pore size distribution and mechanical resistance in sulphide mine tailings, as related to plant habitat requirements. Unaltered tailings, oxidised tailings collected from untreated, fertilized and sludge-amended plots in the field, and mixtures of unaltered tailings and organic amendments prepared in the laboratory, were analysed for pore size distribution. The organic amendments (sewage sludge, peat moss and paper mill sludge) were each applied at the rates of 0, 16 and 33% by volume. A difference in pore-size distribution between untreated and treated samples was shown in both field and laboratory samples. Both inorganic and organic amendments caused a decrease in pores holding water at soil water potentials -10 to -60 kPa, but increased the pores holding water at tensions below -60 kPa. This resulted in a decreased or unchanged content of plant available water (W-a) in all laboratory samples and in the fertilized field samples. Penetration studies in the field showed that additions of fertilizer, without any organic matter, had resulted in hard pans in the oxidised tailings that significantly increased the mechanical resistance in the surface horizon. Thus, this study indicates that the physical influence of the oxidation processes taking place in sulphide mine tailings can be magnified by additions of soil amendments. The aggregation of iron oxides and negatively charged particles such as organic substances or phosphate anions may cement the tailings, which can result in impeded root growth.