Fig. 4. Effect of various combined amendments (hydroxyapatite [HA] + illite and HA + zeolite) on U concentration (A) and pH (B) after equilibrating for 30 d in 0.001 mol L^-1 CaCl₂. Figure C is the subsequent 1.0 mol L^-1 NH₄Cl-extractable U after equilibration. Note that the results for equilibrium (A) and extractable (B) U for the two treatments are essentially identical. Error bars indicate the standard deviation of the means.