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Uptake experiments were carried out with selenate and chromate on fresh and leached Portland and high-alumina cements; and in addition with selenate and selenite on synthetic ettringite. In all experiments with cements, exceptionally high uptake could be observed under conditions where significant amounts of secondary ettringite were formed. Experimental data obtained for pure ettringite corroborated the important role of this mineral phase. However, uptake kinetics show opposite trends in these two systems, which can be viewed as end-members of the same process: Where a fast precipitation of secondary ettringite occurred, initial uptake was high, with Kdvalues in the range of ≍1-5 m3/kg for Se(VI), but decreased with time. Uptake by pre-formed (primary) ettringite initially gave lower Kdvalues (≍0.1 m3/kg), which increased with time. After prolonged equilibration times, the two systems started to approach each other. Concurrent measurements of sulphate concentrations allowed to extract a mean partition coefficient for the solid-solution formation of selenite and selenate with ettringite. Based on this simple solid-solution model, a pragmatic quantitative relation was developed that permits to estimate Kdfor Se(VI) on whole cement as a function of the concentrations of sulphate in the cement and in the solution. A test against experimental data shows reasonably good agreement between measurements and calculations. This relation can also be directly applied to estimate Kdvalues of chromate (and perrhenate) by different cements, indicating the same uptake mechanism. The approach may be less well suited for Se(IV), whose uptake on cement appears to be related mainly to minerals other than ettringite.

The solubility of Sn(IV) in cementitious systems is directly related to the presence of dissolved Ca. In the presence of typical Ca concentrations, solid Ca[Sn(OH)6](s) is precipitated, resulting in dissolved tin(IV) concentrations that are about four to six orders of magnitude lower than observed in alkaline, Ca-free systems. From different experiments carried out in initially oversaturated and undersaturated solutions, solubility products have been evaluated.

Metal uptake and removal from the soil by plants may be a useful measure to remediate contaminated soils. These processes can be enhanced by adding metal chelators to soil. We investigated the effect of nitrilotriacetate (NTA) and urea on the uptake of Cd, Cu, and Zn by lettuce (Lactuca sativaL. cv. Orion) and Italian ryegrass (Lolium perenneL. cv. Bastion) in pot experiments. Nitric acid‐extractable heavy metal concentrations in the contaminated soil were 2 mg Cd, 530 mg Cu, and 700 mg Zn kg−1. Three NTA treatments (0.5, 1.8, and 5.3 mol m−2) were compared with two urea treatments (0.25 and 0.9 mol m−2), and a control. Nitrilotriacetate and urea increased the NaNO3‐extractable soil concentrations of the three metals. At the highest NTA dose, metal concentrations in the aboveground plant biomass was 4 to 24 times greater than in the control plants. While NTA increased plant metal concentrations, it reduced plant matter production. At lower doses, this effect was small. At the highest NTA dose, plant growth was almost completely inhibited. Severe visual symptoms indicated metal toxicity as the likely cause. The urea treatments generally increased the plant matter production. Total metal uptake was in general larger at the lowest or at the intermediate NTA dose than at the highest doses. Little additional total metal uptake was achieved with NTA treatments than with urea. Compared with the controls, neither NTA nor urea enhanced total uptake under the given conditions by more than threefold.