| Zinc is a common heavy metal pollutant. The sludge which is polluted by zinc will cause harm to the natural environment. So it is necessary to choose proper admixtures to solidify and stabilize zinc polluted sludge, improving the engineering properties of zinc polluted sludge and reducing the pollution to the environment. This paper studied the solidification/stabilization effect of cement-based admixtures for Nansha zinc contaminated sludge on the base of the study that named the effect of cement-based admixture mechanical properties of Nansha sludge. Through the unconfined compressive strength test, the leaching experiment, the scanning electron microscope test, the undrainedtriaxial consolidation test, the X-ray diffraction (XRD) test and the dry-wet cycle test, the strength characteristics of the solidified-sludge with different zinc content, the leaching characteristics of the solidified-sludge, the curing mechanism and dry-wet circulation characteristics were preliminary studied. The main contents of this study are shown as follows:(1)Through the unconfined compressive strength test and the leaching test, the solidification/stabilization effect by using cement, cement/lime, cement/bentonite and cement/ground granulated blast furnace slag(GGBS) for different content of zinc contaminated sludge were compared. The results showed that four kinds of cement-based admixtures enhanced the strength of zinc contaminated sludge and reduced the leaching rate of Zn2+. In addition, zinc has an adverse effect on the curing-effect with cement-based admixture, the higher zinc content is, the smaller strength of solidified-sludge will be. Besides, the solidification/stabilization effect of K2 admixture (15%cement+10%GGBS) to zinc contaminated sludge is better than other admixtures.(2)The microstructure characteristics of solidified-sludge solidified by cement, cement/lime, cement/GGBS and cement/bentonite which had different content of zinc were studied by scanning electron microscope (SEM) test. The results showed that at the same content of zinc, the microscopic pore of K2 (15% cement+10% GGBS) solidified-sludge is relatively smaller than others. In addition, Zinc has a bad effect on hydration reaction of cement-based solidified-sludge. The higher zinc content is, the looser micro-structure of the solidified-sludge will be.(3) Shear strength characteristics and stress-strain characteristics of the solidified-sludge with different contents of zinc which were solidified by K2 (15% cement+10% GGBS) admixture were studied by triaxial consolidation undrained test. The stress strain characteristics of solidified-sludge gradually changed from strong strain softening characteristic to weak strain softening characteristic with the increasing content of zinc in the sludge. The cohesive force of solidified-sludge which contained 0-5000mg/kg zinc changed from 608.21kPa to 53.54 kPa and the internal friction angle changed from 41°to 17°.(4) Based on the X-ray diffraction (XRD) test. The impacting mechanism of zinc solidification effect on K2 (15% cement+10% GGBS) admixture was researched. The results showed that zinc will generate precipitation of hydroxide and insoluble hydrate in the hydration reaction of cement and GGBS, which would impede the hydration reaction.(5) Through the wetting-drying cycle test, the mass loss rate of the solidified-sludge and the unconfined compressive strength characteristics along with the change of wetting-drying cycles were studied. The resuls showed that the solidified-sludge of K2 (15%cement+10% GGBS) with different zinc contents had the good durability of wetting-drying cycle, besides, the different zinc content of the unconfined compressive strength of solidified-sludge along with the increase of the number of wetting-drying cycle showed different changing rules. |
PDF Full Text Request