1997 TMS Annual Meeting: Wednesday Session

ALUMINA & BAUXITE TECHNOLOGY: Session III

Session Chairman: David Riner, Reynolds Metals Co., PO Box 9911, Corpus Christi, TX 78469

8:30 am

OPTIMIZATION OF ALUMINA PLANT OPERATION WITH RESPECT TO MARKET CONDITION: P. Das, National Aluminium Company Ltd., Damanjodi, Dist. Koraput, Orissa 763008, India

In international markets, wide fluctuations of alumina prices have been found to be a common phenomenon over the years. It has been observed that almost all the buoyant cycles have essentially been followed by recessionary market conditions. Hence, during the periods when alumina prices are relatively low, for survival it becomes obligatory on the part of the management to strike an operational philosophy suitable for achieving minimum cost of production. However, during buoyant market conditions it is wise to make attempts for maximization of production by suitable optimization of process parameters even if there is a marginal increase in unit cost of production. Since such attempts are directly related to the profitability of the organization, a careful study should be made taking into consideration all interrelated factors. This paper highlights the areas of an alumina plant where changes in process parameters, permissible on technoeconomic consideration, could be made for optimization of production and profitability.

8:55 am

DEVELOPMENT OF SOFTWARE FOR BAYER PROCESS ALUMINA PLANTS: C. Misra, V. Soi, Alumina Technology Associates, 714 Pine Valley Drive, Pittsburgh, PA 15239

PC based software packages have been developed to assist in the operation and management of Bayer process alumina plants. Software packages for digestion, residue washing and precipitation areas have been designed for use by plant operators to formulate operating policy and are integrated with existing or new process control systems. As example, important features and structure of software developed for the precipitation system are discussed in more detail.

9:20 am

DYNAMIC MODELING OF YIELD AND PARTICLE SIZE DISTRIBUTION IN CONTINUOUS BAYER PRECIPITATION: Jerry L. Stephenson, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069; Chris Kapraun, Alcoa Alumina & Chemicals, L.L.C., Point Comfort Operations, State Highway 35, Point Comfort, TX 77978

Process engineers at Alcoa's Point Comfort refinery are using a dynamic model of the Bayer precipitation area to evaluate options in operating strategies. The dynamic simulator, a joint development effort between Point Comfort and Alcoa Technical Center, predicts process yield, particle size distributions, and occluded soda for a given flowsheet of the precipitation and classification circuit. In addition to rigorous material and particle population balances, the model includes mechanistic kinetic expressions for particle growth, agglomeration, nucleation, and attrition. The kinetic parameters have been tuned to Point Comfort's data with excellent matches between the model results and plant data. The model is written for the ACSL package with specially developed input/output graphical user interfaces which provide a user-friendly tool. Features such as a seed charge controller enhance the model's usefulness for evaluating operating conditions and process control approaches.

9:55 am

INCREASING THE ACTIVITY OF SEED USED FOR PRECIPITATION OF THE SODIUM-ALUMINATE LIQUOR: Bi Shiwen, Yang Yihong, Fu Gaofeng, Wen Jie, Ju Aihua, Department of Nonferrous Metallurgy, Northeastern University, Shenyang, 110006, China

The activity of seed is one of the most important factors in the precipitation of the sodium-aluminate liquor. The industrial aluminumoxide-hydrate is treated with sulfuric acid to increase its activity, and then it is used as the seed of precipitation. It is demonstrated that the seed has the ability to increase the rate of precipitation. The reason of this phenomenon is analyzed.

10:10 am BREAK

10:30 am

SECONDARY NUCLEATION OF ALUMINUM TRIHYDROXIDE IN BAYER SODIUM ALUMINATE SOLUTION: Xue Hong, Bi Shiwen, Shuai Shiwu, Yan Yihong, Li Dianfeng, Department of Nonferrous Metallurgy, Northeastern University, China; Chen Wankun, The Great Wall Aluminum Company of China

In this paper, secondary nucleation of aluminum trihydroxide in Bayer sodium aluminate solution was discussed by picture analysis and scanning electron micrograph. The effects of temperature, seed size and aluminate concentration on secondary nucleation are determined with growth time. As this study has shown, the nucleation rate depends upon the experimental conditions of supersaturation, temperature and seed size or surface area. The nucleation can promote the formation of relatively large particles under an opportune condition.

10:55 am

BAYERITE - ALUMINIUM TRIHYDROXIDE: Maurycy M. Pyzalski, Technical University of Mining and Metallurgy, Faculty of Ceramics and Material Engineering, Ave. Micklewicz 30, A-3, 30 - 059 Cracow, Poland

The physico-chemical properties of Bayerite, which was obtained in semi-commercial scale using new technology, were investigated in detail. The properties of another polymorphic form of aluminum trihydroxide, i.e., hydrargillite (Gibbsite) obtained by means of Bayer's and Grzymek's methods were also evaluated in a similar way. The results thus obtained allow characterization of the properties of hydroxides. They also put a new light on their formation and polymorphism.