The Preparation Of Nickel Hydroxide And Nickel Oxyhydroxide By Electrolysis

In this thesis, the method of preparation of spherical a-nickel hydroxide by electrolyzing nickel salts in the electrolysis bath without membrane was reported, and effects on the product's properties under the relative technological conditions have been studied.The method of preparation of nickel oxyhydroxide by oxidizing solid nickel hydroxide in alkaline solution in the electrolysis bath with membrane was also reported in this thesis, and the relationship between current efficiency and technological condition have been studied.The preparation of spherical a -nickel hydroxide by electrolysis is an improvement from the electrodeposit of a -nickel hydroxide, using nickel salts as main electrolyte, with proper complexant. The spherical a -nickel hydroxide with tap density exceeding 1.5g/ml can be obtained in the electrolysis bath. It seems that: (l)Stirring and existing of complexant which is ammonium or ammonia are essential factors to get a -Ni(OH)2. Without complexant, a -Ni(OH)2 cannot be obtained by electrolyzing solution of NiCl2, Ni(NO3)2, NiSO4 , NiCl2+NiSO4 and Ni(NO3)2+NiSO4 at any concentration. (2)If the mixture of nickel chloride and nickel nitrate is used as electrolyte, only when the concentration of total nickel between 0.6mol/l and 0.9moI/I and the ratio of nickel chloride and nickel nitrate around 1:5, a -Ni(OH)2 can be produced. (3)When ammonium salts or ammonia being complexant, a -Ni(OH)2 grain can be made by electrolyzing solution of NiCI2, Ni(NO3)2, NiSO4, NiCl2+NiSO4 , Ni(NO3)2+NiSO4 and NiCl2+Ni(NO3)2 at the concentration range of total nickel being 0.5mol/l to 1.0mol/1. (4)The effect of electrolysis can be excellent when the ratio of NH4+ to Ni2+ (NH4+/Ni2+) is between 0.5 and 2.0, at which not only spherical a -Ni(OH)2 can be obtained, but also waste of sources caused by long-time electrolysis can be avoided. (5) While keepingother technological conditions, the increasing of electrolysis time has great effects on the properties of the product. With the extending of electrolysis time over 65h, the tap density of Ni(OH)2 increases from under 1.0g/ml to over 1.5g/ml. Moreover, Ni(OH)2 becomes more and more regular in form. It is important to point out that the above tendencies become slower, when the electrolysis proceed more than 60h. (6)The XRD and IR show that the Ni(OH)2 produced by the method mentioned above is a -Ni(OH)2, and the method has great technological stability.The preparation of nickel oxyhydroxide by electrolysis which oxidation occurs on the anode electrode in the alkaline solution used to be electrolyte, and electrolyte and the electrodes can be reused. This method, overcoming shortcomings of the chemical method, is an ideal method to produce pure nickel oxyhydroxide and wastes little. The conclusion can be drawn:(1) The best shape of electrolysis bath is cylinder, and membrane must be used.(2) Stirring is an essential factor. The higher current efficiency can be got under those conditions, which are concentration of electrolyte being between 30% and 40% and adding 125g Ni(OH)2 to 300ml electrolyte(the ratio of solid to liquid). (3) The current efficiency is the highest by 2A. (4) The KOH electrolyte is better than NaOH electrolyte. The electrolysis effect will be much better if a few LiOH is added to KOH electrolyte. (5) The specific surface area of NiOOH is the smallest when NiOOH with midest oxidity. (6) Two types of Ni(OH)2, which are pure Ni(OH)2 and Ni(OH)2 coated with 6% Co(OH)2, were compared in electrolysis effect, and there are no difference between them.(7) The XRD shows that NiOOH is made of Ni( II ),Ni( III ) and Ni(IV), and the content of -NiOOH increases with the oxidity of NiOOH increasing.