The invention relates to a method of separating a particle fraction from a particle stream making use of gravitational force and which is performed in a fluid. This provides particle fractions that are collected in respective collecting means. According to the invention the fluid and the collecting means are moved in relation to each other defining a relative direction of movement. There are means provided to limit the movement of the particles to be separated with respect to the fluid in the relative direction of movement. The invention also relates to an apparatus for carrying out the method.

A method of reblending sand in a classification tank (10) having multiple stations (14A-J) and discharge valves (16A-C) within each station includes the steps of delivering sand to the tank (10); calibrating the tank to analyze the raw feed material and develop discharge rates, flow multipliers, and a mathematical model of the tank; and inputting a specification or quantity and sieve size distribution for a reblended sand product into a computer (20) for controlling the tank (10). Then the tank (10) is operated in a production mode and the discharge valves (16A-C) at each station of the tank (10) are adjusted by the computer (20) for percent open time and discharge rate. With one algorithm, the computer (20) identifies which station (14A-J) has the most of a sieve size that is out of specification and diverts material at that station by closing the appropriate discharge valve(s) (16A-C). In another algorithm especially adapted to minimize fines, the computer (20) begins with the station (14A-J) most remote from the inlet and diverts material by repeatedly reducing the valve (16A-C) open percentage of the appropriate valve (16A-C) at that station (14A-J) by a given amount until the specification is met or the valve (16A-C) is always closed. Once the valve (16A-C) is always closed, the computer (20) moves a station (14A-J) closer to the inlet and repeats the process. Once a primary product is being produced to specification, the same algorithm can be used to control the production of a secondary product.

The process comprises: a) introduction of the precious metals, in the form of laminas, leafs or wafers in a container provided with grinding means; b) addition to said container with the precious metal of a liquid medium of a density between 0.61 g/ml and 1.50 g/ml at room temperature; c) grinding of the precious metal in the container, in the presence of the liquid medium, until the former is transformed into a product consisting of precious metal particles of the desired size; d) allowing said particles to sediment; e) extraction of the liquid medium; and f) removal of the precious metal transformed into fine particles with an average size between 0.00020 mm- and 0.6 mm², completely dry. These particles can be added to a liquid medium such as a perfume, an essence, cava, champagne, liquor, edible oil, paint or the like.