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The objective of the present investigation was to elucidate the time‐dependence of phosphate adsorption by calcium carbonate and Ca‐kaolinite and to suggest a mechanism of adsorption. The phosphate adsorption by calcium carbonate and Ca‐kaolinite at low phosphate concentrations in solution could be described by Langmuir adsorption isotherms, indicating that a monolayer of phosphate is formed on the surface. The calculated maximum surface saturation was 25µg/g for calcium carbonate and 187µg/g for Ca‐kaolinite. A second‐order kinetic equation was developed which considers both the change in phosphate concentration in solution and the surface saturation of the adsorbent during the adsorption process. The rate constant of phosphate adsorption was about 30,000 times greater for calcium carbonate than for Ca‐kaolinite. About 80% of the phosphate adsorption by calcium carbonate was completed within 10 sec. The variation of the second‐order rate constant with phosphate concentration was different in the two systems. The rate constant decreased in the calcium carbonate‐phosphate system and increased in the Ca‐kaolinite‐phosphate system with increasing phosphate concentration. It was suggested that phosphate ions are adsorbed by displacing coordinated water molecules and/or coordinated anions.

The objectives of the present investigation were to gain information on the rate and extent of phosphate adsorption and desorption and the energy of phosphate adsorption by lake sediments, and to evaluate the influence of the sediments on the phosphorus status of lake waters. While phosphate adsorption by sediments from Sebasticook Lake, Maine, could be described by the Freundlich equation over a large phosphorus concentration range, the Langmuir equation provided a good fit to the experimental data only at low phosphorus concentrations. The deviation from the Langmuir isotherm at high phosphorus concentrations was explained by an increase in total negative potential of the surface due to phosphorus adsorption and increased interaction between adsorbate molecules. The rate of phosphorus adsorption by the sediments could be described by the equation X = KC0t1/m. The calculated activation energy was 2.7 kcal/mole.The desorption of phosphorus from minerals and sediments was dependent on the anionic species present in the solution. The replacing power of the anions appeared to be related to their ionic potential and complexing ability. The rate of phosphorus desorption could be described by the proposed kinetic equation.

At Risdalsheia (southern Norway), an ongoing catchment-scale acid-exclusion experiment has been conducted since 1984 as part of the RAIN project (Reversing Acidification In Norway). Acid precipitation is collected on a 1200-m2 transparent roof, treated by ion exchange, sea salts readded, and reapplied as clean rain beneath the roof Up to 1990 annual surveys of soil chemistry have revealed no significant trends. The chemical composition of runoff has changed: sulfate decreased from about 111 μeq/L in 1984 to 38 μeq/L in 1992 and nitrate from about 33 to 5 μeq/L. Base cations decreased and alkalinity increased over the 8-yr period from −88 to −29 μeq/L to compensate for this change in strong acid anions. Much of the alkalinity change is due to the increased role of organic anions. The results fit an empirical nomograph relating alkalinity, base cations, and strong acid anions and a new empirical nomograph relating alkalinity, H+, and total organic carbon. The acid-exclusion experiment provides the first catchment-scale evidence for the reversibility of nitrogen saturation; RAIN results corroborate field observations of changes in surface water chemistry in response to reduced acid deposition as well as process-oriented, conceptual acidification models.