The effect of pH upon the copper and cupric ion concentrations in soil solutions

Abstract

Soil samples whose pH had been adjusted to between 4.5 and 7.5 either for long periods in the field or short periods in the laboratory were incubated after wetting with water or 0.01 M CaCl2. Copper concentrations in the soil solutions decreased only slightly as the solution pH increased, but free cupric ion concentrations decreased considerably. The copper concentrations were smaller and the proportion of copper present in solution as cupric ion at a given pH was larger when CaCl2 rather than water was used. Complexed organic species made up most of the copper in all solutions. The duration of pH adjustment did not affect these results.Copper adsorption isotherms were determined on the soils using low equilibrium solution concentrations. As a given copper concentration the quantity of copper adsorbed increased and the proportion of copper in solution present as cuprk ion decreased with pH increase; again the duration of pH adjustment did not affect the results. IntroduclionA knowledge ofthe concentration and form ofa trace element in the soil solution and the factors that control these is essential for understanding the mechanisms of its uptake by plants. Determination of the free metal ion concentration is of fundamental importance because this species enters into all equilibria between different forms of the metals in solution. This paper describes measurements of the effect of pH upon the distribution of copper between the solid phase, complexed copper species in solution, and the free cupric ion, in a series of samples from plots whose pH had been adjusted in the field to between 4.5 and 7.5 over a long period. Similar measurements were made on samples of the same soil whose pH had recently been altered in the laboratory to see whether the duration ofa pH change affected the distribution of copper.Determinations of adsorption isotherms were made on the same soil samples in order to study the combined effects of pH and amount of added copper on the equilibrium between solid-phase copper, complexed copper species in solution, and free cupric ions. E.rperimenta1The soils used were samples of a sandy loam (Marcham series) from Kennington Extension Forest Nursery, Berkshire, where plots were laid down in 1948 to observe 679

Copper availability as related to soil copper fractions in oxisols under liming

“…These results indicate a high Cu adsorption capacity of the soils and are in agreement with Msaky & Calvet (1990) that observed complete adsorption of the Cu added to soil, even at low pH. On the other hand, the elevation of soil pH above 5.0 resulted in decrease of Cu concentration in solution (Sanders, 1982), which indicates the influence of higher pH values on the Cu sorption to the soil. The metals with higher electronegativities form stronger covalent & Crawford, 1973a;Shuman, 1985;Sims, 1986).…”

Reactions Controlling Heavy Metal Solubility in Soils

“…Estimating the level of soluble Ca2+ at about 10-3 M and assuming that all soil Cu 2 + is exchangeable, one would estimate a Cu 2 + solubility in these soils to be about 10-5 M from equation 2. The much lower solubilities obtained in reality (Sanders, 1982) lead to the obvious conclusion that mechanisms much more specific than ion exchange are needed to explain the behavior of Cu and other heavy metals. In fact, evidence for specific adsorption of metals such as C02+, Zn 2 +, and Cd2+ (Hodgson, 1960;Tiller and Hodgson, 1962;Page, 1976, 1977) has been obtained for very low adsorption levels on layer silicate clays.…”

Fractionation of lead-acid battery soil amended with Biochar

“…Soil pH is the most widely accepted parameter which exerts a controlling influence on the availability of micro-nutrients and heavy metals in the soil to plants (Sanders, 1982;Igwe et al, 2005). Banjoko and Sobulo, (1994) reported that some Nigerian soils especially in the forest and savannah regions are within a pH range of 5.70 -6.50.…”