THE RESEARCH PROJECT AIMS AT UTILIZATION OF THE VAW TUBE DIGESTER UNITS FOR INDUSTRIAL SCALE PROCESSING OF GREEK DIASPORE BAUXITE, THUS IMPROVING THE ECONOMIC OF THE CONVENTIONAL BAYER PROCESS. A NOVEL FEATURE OF THE PROCESS IS INDICATED BY REDUCED ENERGY CONSUMPTION FOR DIASPORE DISSOLUTION FROM BAUXITE DUE TO HIGHER TEMPERATURE.

THE BEHAVIOUR OF GREEK DIASPORE BAUXITES DURING DIGESTION IN THE VAW MIDIFIED BAYER PROCESS (DIGESTION IN THE TUBE REACTOR) WILL BE TESTED ON LABORATORY AND INDUSTRIAL SCALE :

A) LABORATORY TESTS : APPROX. 50 KG-SAMPLES OF BAUXITES ARE EXAMINED TO DETERMINE THE CHEMICAL AND MINERALOGICAL CHARACTERISTICS AND TO OBSERVE THE BEHAVIOUR UNDER THE DIGESTION CONDITIONS. SIMILARELY, THE COMPOSITION AND SEPARATION CHARACTERISTICS OF THE RESIDUE (RED MUD) AND LIQUOR CLARIFICATION WILL BE EXAMINED.

B) INDUSTRIAL-SCALE TESTS : ONE PLANT UNIT IN THE VAW LIPPEWERK WILL BE OPERATED TEMPORARILY FOR ABOUT 1.500 OPERATING HOURS TO PROCESS APROX. 70.000 MT OF RAW BAUXITE FROM GREECE. THE INDUSTRIAL-SCALE OPERATIONS REFER MAINLY TO

- GRINDING OF THE BAUXITE,
- DIGESTION IN THE TUBE REACOR AT TEMPERATURE UP TO 280 C AT VARIABLE RETENTION TIMES AND VARYING SOLID/LIQUID-RATIOS IN THE DIGESTED SUSPENSION,

- SEPARATION OF RED MUD BY SEDIMENTATION AND FILTRATION,

- DETERMINATION OF OPTIMUM TUBE DIGESTER AVAILABILITY FOR THE BEAUXITE PROCESSED IN IT.

C) EVALUATION OF THE TESTRUNS : TESTS AS PECIFIED UNDER A) AND B) WILL BE USED TO DETERMINE
- GRINDING BEHAVIOUR,
- SPECIFIC CONSUMPTION OF BAUXITE, ALKALI AND WASH WATER,
SPECIFIC CONSUMPTION OF THERMAL ENERGY, CORRESPONDING TO THE ENERGY-SAVING CONCEPTION OF THE VAW TUBE REACTOR
- OPTIMUM DIGESTION CONDITIONS, I.E. TEMPERATURE, RETENTION TIME, MOLAR RATIOS, AND YIELD,
- SPECIFIC QUANTITY OF RED MUD GENERATED, AS WELL AS ITS SETTING AND FILTRATION BEHAVIOUR.