Water for gold mining operations has been obtained by deep, shallow, and artesian wells; mines; mined out open pits; springs; and rivers. Some wells have provided hot water from muddy and debris-laden river water. One such plant takes water from a river, which carries a varying, but always substantial percentage of earthen solids as well as debris such as twigs, weeds and others. The intake device may be a concrete tower with a number of gates at different levels which could be opened or closed from the top of the tower. For any level of the river a gate could be selected which could be above the very coarse material riding the bottom and below the floating debris on the surface.
Trash screens serves to keep out large pieces of debris. Water is pumped from the tower by a submerged pump to a degritter that is a large hydraulic cyclone employed to remove coarse material which are removed to the river. From this point, the water can flow by gravity to a clarifier tank, which removes most of the remaining solids with the underflow returning to the river. The overflow is transported by gravity to an alumina-gel clarifier in which the gel is produced by continuous feeding of alumina and lime. The overflow is sent to a surge tank and storage tanks located above the mill site. At this point the water is satisfactory for mill requirements and fire protection. Chlorination is required due to healthy aspects when is necessary potable water. For table water, the tank storage water is pumped through gravel filters and softened. Further chemical treatment can be considered for any special requirements such water for boilers employed in activated carbon desorption plants.
In addition to storage tanks for process and potable water, it is common practice to have storage capacity for fire protection water, with rigid rules that this reserve must not be employed for any other purpose. Often this will be kept in the same tank with process water, the latter being drawn off through a standpipe, with the fire protection water outlet being at the bottom of the tank and usually piped throughout the mill in separate lines. Most of the variations in new water requirements are due to the type of process in use and the consumption may vary from as low as 100 to as high as 10,000 gallons per ton of ore. Alkaline processing needs less water than acid since the operations are in closed circuit. Other factors which influence water usage include the extent to which new water is employed for cleanup, to repulp tailings for pumping, the circuit solution bleed requirements, evaporation losses and the extent to which solutions are reclaimed for reuse. The latter could include the recycle of barren solutions.