This paper describes the development of a new type of rotary air valve which has been done in order to increase the capacity and efficiency of an air-pulsated jig.
This new rotary air valve is characterized by having an exhaust port and two inlet ports which admit high and low pressure airs separately.
It can realize a desired water pulsation best suited for the separation and stratification of raw coal.
The development of the valve design is based on the theory presented by the authers at the 8th International Coal Preparation Congress.
Numerical analysis were conducted to obtain the optimum port area diagram of air valve.
To confirm the results, experiments were carried out on a model jig.

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The relation between the zeta potential of coal fine-particles and pH value of suspension in aqueous suspension for different kinds of coal samples was determined by using a rectangular micro-electrophoresis cell.
The empirical equation of the relation between the zeta potential of the particles and the chemical components of coal samples was determined in aqueous suspension of different pH values. The equation is represented as follows :
Z=Bc×(C)+BH×(H)+Bo×(O)+BN×(N)+Bs×(S)+BA×(ASH), where Z is the zeta potential of the particles, (C), (H), (O), (N), (S) and (ASH) are weight percent of carbon, hydrogen, oxygen, nitrogen, sulphur and ash, respectively, and BC, BH, BO, BN, BS and BA are coefficients of each of the respective components of coal samples.
The above coefficients were calculated numerically by the least square method in suspensions with different pH values. The values of the coefficients, Bc, BH, etc. (mV/%), indicate the zeta potential of each respective single component; viz, carbon, hydrogen, etc. of the coal samples. When the chemical components of a coal sample are known, the zeta potential of the coal fine-particles can be determined by the equation with the coefficients obtained in suspensions with different pH values.

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It is important to determine the zeta potential and the particle size distribution of mineral particles in suspension for the investigation of flocculation and dispersion phenomena which have been applied with advantage in mineral processing and in a number of solid/liquid separation processes. We proposed an improved method for determining the zeta potential of mineral particles by micro-electrophoresis. We developed an improved sedimentation balance for particle size distribution analysis of mineral particles in suspension. The particle size distribution curve of suspended particles in aqueous suspensions of quartz, fluorite and a mixture of equal weights of both particles was determined by using the sedimentation balance in order to investigate the flocculation and dispersion phenomena relating to the zeta potential of mineral particles determined by our method. Whereas quartz and fluorite particles dispersed in separate acid suspensions of pH about 7 or less, a mixture of equal weights of both quartz and fluorite particles flocculated in a third suspension of pH about 10 or less. This phenomenon is possibly explained by the heterofloccu-lation of quartz and fluorite particles which are respectively negatively and positively charged in the suspension of pH about 10 or less.

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The influence of pH and the concentration of dispersants on the coagulation and dispersion of fine particles in water is mainly dealt with in this paper.
By using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the bulk zeta potentials at pH values, the coagulation values are obtained. The analytical results are compared with the experimental ones obtained using red mud, roseki and talc as well as with data in the literature. As a result, the calculated and experimental values are found to be nearly coincident except for clays like kaolinite and it is proposed in the case of kaolinite that the heterocoagulation between the face and edge of the clay must be taken into account in the acidic region. By using the coagulation phenomenon, red mud is also shown to be removed from suspensions by means of the deep bed filtration.
An experimental method of finding the optimum concentration of a dispersant is proposed. Then, the influence of pH and the concentration of dispersants on the dispersion of fine particles in water is analyzed by using the DLVO theory. As a result, it is found that the optimum concentration of a dispersant determined experimentally is approximately in accordance with the concentration of the dispersant showing the maximum total potential energy calculated from the DLVO theory.

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The Tahmoor mine is located some 80 km south-west of Sydney in the South Western coal mining district of New South Wales.
Construction of the Coal Preparation Plant was completed in June 1981. Since this time the plant has processed all run of mine production on a two shift per day basis.
The plant is a nominal 300 tonne per hour single module unit. Plant design consists of jig washing and froth flotation of the fines, with the option of dense medium separation if the raw coal quality warrants the production of a middlings product.
From an engineering point of view the special features of the Tahmoor Plant are:-
1. The Baum jig has 10 compartments and three elevators. This allows middlings recycling in the third elevator.
2. The Leebar bath was selected because of its capability for a low S.G. cut and its mechanical reliability.
3. The selection of an Enviroclear thickener for tailings thickening.
4. A mechanical tailings dewatering plant which includes a solid bowl centrifuge and a band press filter. Major emphasis is placed on all aspects of quality control and plant efficiency. This is reflected in the consistency of product and reliability in operation of the plant.

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