Study On The Process Of Preparing Superfine Bismuth Oxide Using Silver-zinc Slag With High Bismuth Content As Raw Material

Being a kind of "green metal", the bismuth can be used extensivelyin many aspects. Our country owns abundant resources of bismuth, andthe annual production of bismuth take the first place in the world.However, because of having lower technology content, our products'competition ability on the international market is not strong. As a result,most of the bismuth products are exported in the form of bismuth ingots.So it is great significant to exploit the bismuth chemical products withhigh additional value.In this dissertation, the technology of extracting bismuth fromsilver-zinc slag has been studied, using the silver-zinc slag with highbismuth content of a company as raw material. Bismuth has been distilledby hydrolytic precipitation method and made into a high purity bismuthoxide. The process of preparing superfine bismuth oxide by chemicalprecipitation method has been studied and the problem of control ofparticle size during this process has been discussed. At the same time thepreliminary exploration on the preparation of superfine bismuth oxide byhydrothermal method has also been carried on.The optimum technological conditions of extracting silver-zinc slagare as follows: The liquid to solid ratio is 8～10, the dosage of NaClO₃ is10～15g/L, the dosage of NaCI is 60g/L, hydrochloric acid dosage is80～100 ml/L, reaction temperature is 70～80℃, reaction time is 4～5 h.The base metals such as Bi were extracted basically under such condition,while the Au and Ag were enriched in the slag.Under the indoor temperature, the precursor deposition was preparedby adopting an anti-toward way of drop wise and controlling thetechnological conditions as follows: Bi(NO₃)₃ concentration is0.3mol/L,ammonia concentration is 1: 10, the Bi(NO₃)₃ adding rate is2.5 ml/min, the end-point pH value is 9 or so, stirring speed is 600 r/min.Then the precursor was dried at 100℃for 2 hours and calcined at 600℃for 2 hours. A monoclinicα-Bi₂O₃ superfine powder taking around-thin-slice shape has been obtained. The grain size is relatively even, with an average diameter and thickness of lμm and 0.2μmrespectively. The appearance of the product has a bright color of orange.The reasons causing the growth and conglobation of the grainsduring the process of preparing superfine bismuth oxide using chemicalprecipitation method has been analyzed. The growth and conglobation ofthe grains were controlled effectively by means of adopting vary-velocitydropwise method and adding surface active agent during the precipitationstage, and dealing with the precursor by washing it with ethanol andazeotropic distilling with normal butyl alcohol, thus a fine dispersedsuperfine bismuth oxide with an average particle size of 0.116μm.The exploration experiments on the preparation of superfine bismuthoxide by hydrothermal method has been carried on.the result shows that:the factors such as react temperature and time, filling degree of solvent,pH value and type of react medium have great effects on the particlesize and shape of the bismuth oxide crystal prepared by hydrothermalmethod. Increasing react temperature and extending react time will leadto an increase in the average particle size and the breadth of the particlesize distribution, while increasing the filling degree of solvent maydecrease the average particle size. Particles with different shape (such asthin-slices, needles, thread etc.) can be prepared respectively underdifferent pH value. And superfine bismuth oxide with differentcrystallographic form (e.g.α,βetc.)may be obtained by altering the typeof react medium.