This research studied the influence of individual heavy metal on the hydration reactions of major cement clinker phases in order to investigate the performance of cement based stabilization/solidification (S/S) system. Tricalcium silicate (C3S) and tricalcium aluminate (C(3)A) had been mixed with individual heavy metal hydroxide including Zn(OH)(2), Pb(OH)(2) and Cu(OH)(2), respectively. The influences of these heavy metal hydroxides on the hydration Of C3S and C(3)A have been characterized by X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). A mixture of Zn(OH)(2), Pb(OH)(2) and Cu(OH)(2) was blended with Portland cement (PC) and evaluated through compressive strength and dynamic leach test. XRD and DSC-TG data show that all the heavy metal hydroxides (Zn(OH)(2), Pb(OH)2 and Cu(OH)(2)) have detrimental effects on the hydration Of C(3)A, but only Zn(OH)(2) does to the C3S at early curing ages which can completely inhibit the hydration Of C3S due to the formation of CaO(Zn(OH)(2))(.)2H(2)O. Cu(6)Al(2)O(8)CO(3)(.)12H(2)O, Pb2Al4O4(CO3)(4)(.)7H(2)O and Zn(6)Al(2)O(8)CO(3)(.)12H(2)O are formed in all the samples containing C(3)A in the presence of metal hydroxides. After adding CaSO4 into CA the detrimental effect of heavy metals increases due to the coating effect of both calcium aluminate sulphates and heavy metal aluminate carbonates. The influence of heavy metal hydroxide on the hydration of C3S and C(3)A can be used to predict the S/S performance of Portland cement. (c) 2006 Elsevier B.V. All rights reserved.