Dissolution rate determination of alumina in molten cryolite-based aluminum electrolyte

Abstract

Determination of dissolution rate of alumina is one of the classical problems in aluminum electrolysis. A novel method which can measure the dissolution rate of alumina was presented. Effect of factors on dissolution rate of alumina was studied intuitively and roundly using transparent quartz electrobath and image analysis techniques. Images about dissolution process of alumina were taken at an interval of fixed time from transparent quartz electrobath of double rooms. Gabor wavelet transforms were used for extracting and describing the texture features of each image. After subsampling several times, the dissolution rate of alumina was computed using these texture features in local neighborhood of samples. Regression equation of the dissolution rate of alumina was obtained using these dissolution rates. Experiments show that the regression equation of the dissolution rate of alumina is y=−0.000 5x³+0.024 0x²−0.287 3x+ 1.276 7 for Na₃AlF₆-AlF₃-Al₂O₃-CaF₂-LiF-MgF₂ system at 920 °C.

Keywords

aluminum electrolyte / dissolution rate / image analysis / alumina / Gabor wavelet transform

References

[1] SolheimA., RolsethS., SkybakmoenE.. Liquidus temperature and alumina solubility in the system Na₃AlF₆-AlF₃-LiF-CaF₂-MgF₂ [C]. Light Metals 1995, 1995, Warrendale, Minerals, Metals & Materials Soc: 451-456

[2] KellerR.. Alumina dissolution and sludge formation revisited [C]. Light Metals 2005, 2005, Warrendale, Minerals, Metals & Materials Soc: 147-150

[3] HaverkampR. G., WelchB. J.. Modelling the dissolution of alumina power in cryolite [J]. Chemical Engineering and Processing, 1998, 37: 177-187

[4] SkybakmoenE., SolheimA., StertenA.. Alumina solubility in molten salt systems of interest for aluminum electrolysis and related phase diagram data [J]. Metallurgical and Materials Transactions B, 1997, 28B(2): 81-86

[5] GerlachJ., HennigU., KernK.. The dissolution of aluminum oxide in cryolite melts [J]. Metallurgical Transactions B, 1975, 6B(3): 83-86

[6] WelchB. J., GerdaI. K.. Crust and alumina powder dissolution in aluminum smelting electrolytes [J]. JOM, 2007, 59(5): 50-54

[7] ZhangY. S., WuX. X., RobertA. R.. Solubility of alumina in cryolite melts: Measurements and modeling at 1 300 K [J]. Metallurgical and Materials Transactions B, 2003, 34B(4): 235-242

[8] YangZ.-h., GaoB.-l., XuN., QiuZ.-x., LiuY.-kuan.. Dissolution of alumina in molten cryolite: A video recording study [J]. Journal of Northeastern University: Natural Science, 1999, 20(4): 398-400

[9] XuJ.-l., ShiZ.-n., GaoB.-l., QiuZ.-xian.. Dissolution of alumina in molten cryolite [J]. Journal of Northeastern University: Natural Science, 2003, 24(9): 832-834

[10] QiuZ.-x., WangZ.-w., GaoB.-l., YuX.-guang.. Physical and chemical processes of low temperature aluminum electrolysis [J]. Mining Research and Development, 2003, 8: 9-12

[11] FanL.-m., QiuZ.-x., GrjotheimK.. A direct observation of the process of aluminium in cryolite-alumina electrolyte through a transparent quartz cell [J]. Journal of Northeastern University, 1986, 46(1): 97-106

[12] XuJ.-l., ShiZ.-n., GaoB.-l., QiuZ.-xian.. Bubble behavior on metal anode of aluminum electrolysis [J]. The Chinese Journal of Nonferrous Metals, 2004, 14(2): 298-301

[13] KanH.-m., ZhangN., WangX.-yang.. Study on solution of Al₂O₃ in low temperature aluminum electrolyte [C]. Light Metals 2011, 2011, Warrendale, Minerals, Metals & Materials Soc: 503-507

[14] ZhangG., MaZ. M., DengL.-g., XuC.-ming.. Novel histogram descriptor for global feature extraction and description [J]. Journal of Central South University of Technology, 2010, 17(3): 580-586

[15] MaZ. M., ZhangG., YanLi.. Shape feature descriptor using modified Zernike moments [J]. Pattern Analysis and Applications, 2011, 14(1): 9-22

[16] YangY.-j., WangZ.-w., FuW.-q., GaoB.-l., HuX.-w., YuY.-x., LiuY.-le.. Dissolution behavior of alumina in molten aluminum electrolyte [C]. World Non-Grid-Connected Wind Power and Energy Conference (WNWEC), 2010, Nanjing, INSPEC: 1-6