The different cadmium (Cd) contaminated (1.0 and 10.0 mg/L) soils were simulated in laboratory. And the effects of fixed addition of biochar and zeolite (1:1) on soil pH and the changes of Cd morphology were studied. The addition amounts of the mixture were low (0.4%)

medium (2%) and high (10%)

respectively. Results showed that the values of pH were higher in the contaminated soil than the control

and increased with the increasing addition amount of mixture. With the increasing?incubation?time

the value of pH was gradually decreased in the lowly contaminated soil

whereas increased earlier

then decreased

and finally stable in the highly contaminated soil. In the late stages of incubation

the decreased percentages of effective Cd with the mixture addition of 2% and 10% were highest for the lowly contaminated and highly contaminated soil respectively

i.e. 56.78% and 27.33%. The exchangeable Cd percentage was gradually increased with the addition of biochar and zeolite mixture in soil. The percentages of exchangeable Cd were reduced by 8.35%

13.81% and 20.65%

respectively

compared with the control soil in the lowly contaminated soil

and by 10.02%

22.34% and 33.01%

respectively in the highly contaminated soil. The contents of exchangeable Cd could be reduced in soil with the passivation agent

through increasing the Cd contents of Carbonate bound

Fe-Mn oxide-bound

organic-bound and residual Cd. The Cd content of organic-bound Cd was higher in the lowly contaminated soil than the highly contaminated soil. Thus

the fixed addition of biochar and zeolite could reduce the bioavailability of heavy metals in soil

providing a theoretical foundation for farmland soil remediation.