A spiral separator including an upright column and supportable with its axis substantially vertical which is adapted to receive at an upper end thereof a pulp of water and particles to be separated, said spiral separator comprising a continuous helical trough section mounted on said upright column wherein at least in the top portion of the trough there is provide a channel which is initially narrow and deep and becomes progressively wider to enable the particles to obtain or maintain an initial velocity so as to maintain the flow of pulp without the coarser and/or less dense particles becoming stationary or standing and wherein the coarser and/or less dense particles may be retained in an outer section of the trough and the finer and/or denser particles may move towards an inner section of the trough and be retained in said inner section.
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