Abstract
By the use of synthetic nickelferrite, nickelaluminate, nickelsilicate and their mixed salts, the relation between the fractional reduction of the sample and the extraction of nickel in a NH3-(NH4)2SO4 solution have been examined under the condition of pressure leaching. A wet process was adopted for the syntheses of nickelferrite, nickelaluminate, nickelsilicate and their mixed salts. Purified carbon monoxide and hydrogen were used as the reducing gases. The results obtained are summarized as follows:
(1) The reduction of nickelferrite with carbon monoxide gradually proceeds with increasing time of reduction. On the other hand, the reduction of nickelaluminate and nickelsilicate rapidly proceeds with increasing time of reduction at an early stage of reduction.
(2) The fractional reduction of the sample synthesized is effect mainly with the reduction temperature rather than the gaseous composition, the time of reduction and the flow rate of reducing gas.
(3) Nickelferrite, nickelaluminate and nickelsilicate do not dissolve in the NH3-(NH4)2SO4 solution under the condition of pressure leaching.
(4) Nickel in nickelferrite is selectively reduced during the roasting. On the contrary, nickel in nickelaluminate, nickelsilicate and their mixed salts are not selectively reduced during the roasting. Then, the extraction percentage of nickel after the roasting is in the order of nickelferrite>nickel-aluminate>nickelsilicate.
(5) Under the condition of ammonia pressure leaching, it is required for efficient extraction of nickel that each compound synthesized should be fully reduced during the roasting.
