Abstract: After 105 d continuous static soaking tests，the variation rule of the pH value of the soaking solutions and the ion concentration with soaking time for a molybdenum tailing is investigated.The results showed that this tailing can well neutralize the acidic solutions of pH values ranged from 3.5 to 6 to neutral state (pH=7) within 2~8 days and then always maintained this state.The more fine the tailing is，the more thick the Ni²⁺ ion release solution is.In general，Ni²⁺ ionic concentration reached its maximum values within 25 d，and then declined，following with oscillating around some average values.

Key words: Molybdenum tailings, Static soaking, pH value, Ni²⁺ Ion release thickness