Neutralization method and neutralization plant

A neutralization method used in a neutralization step of neutralizing leachate produced by leaching nickel oxide ore, and producing neutralized sediment containing impurities and a post-neutralization solution containing zinc together with nickel and cobalt, in a hydrometallurgy process for nickel oxide ore, the method comprising:

• a neutralization reaction step of neutralizing the leachate in a neutralization reaction tank;
• a separation step of separating neutralized slurry into neutralized sediment and the post-neutralization solution by adding flocculant to the slurry;
• a viscosity measuring step of measuring the viscosity of the post-neutralization solution produced through the separation step;
• a storing step of temporarily storing the post-neutralization solution in a storage tank;
• and
• a flow-feeding step of transferring the stored post-neutralization solution to a dezincification reaction tank used in a dezincification step subsequent to the neutralization step,
• wherein in the flow-feeding step, when the post-neutralization solution has a viscosity, as measured in the viscosity measuring step such that the rate for passing 50 mL of the post-neutralization solution through a membrane filter having a mesh opening size of 0.45 μm, that is higher than 0.10 sec/cm2·mL, a flow rate of the post-neutralization solution to be transferred to the dezincification reaction tank is controlled, and the post-neutralization solution is circulated by returning back a predetermined rate of the post-neutralization solution to the neutralization reaction tank,
• and when the viscosity of the post-neutralization solution measured in the viscosity measuring step is higher than 0.10 sec/cm2·mL, a flow rate of the post-neutralization solution to be transferred to the dezincification reaction tank used in the dezincification step is set to 60 to 80% for the total flow rate, and a flow rate of the post-neutralization solution to be circulated by returning back the post-neutralization solution to the neutralization reaction tank is set to 20 to 40% for the total flow rate.