Abstract: The kinetics of extraction erhium(Ⅲ)from sulphurib acid solutions with HEHl[EHP]in n-heptane has been investigated. The effects of the concentrations of Er³⁺,H⁺,SO₄^2-,and HEH[EHP]on the extraction rate for Er(Ⅲ)have been observed. It is found that therate of forward extraction reaction is proportional to [Er³⁺], [H⁺]^-2.25,[SO₄^2-]^0.26 and[H₂A₂]_(o)^1.69,white the rate of backward extraction reaction is proportional to [Er(Ⅲ)]_(o),[H⁺]^1.05and [H₂A₂]_(o)^-1.08.The rate-determining step is suggested to be the chemical reactionof ErA₂ with HA at the interface for forward extraction and H⁺ with ErA_3(o) at the inter-face for backward extraction.

Key words: erbium, HEH[EHP], extraction, kinetics