If a column of something like chalk was put in a long pipe and sea water poured in to it would that remove the

Question

salt and other impurities etc etc.

Answer 1

It would filter out any solid particles like dirt, sand, algae, plankton, and probably most of the bacteria (depends how long it is and how tightly packed the chalk is).

It will not remove any salts from the water because dissolved substances cannot be removed by filtering.

Answer 2

If you mean chalk specifically running sea water through it will eventually dissolve it (I am assuming it has some porosity and permeability, which chalk normally does).  How fast is dependent on the temperature.  Calcium carbonate is one of the odd compounds that has its highest solubility  at low temperatures, a few degrees above O degrees C.  As the temperature goes up its solubility decreases.   This is part of why coral reefs are in tropical waters, in warm water it is easier to precipitate the CaCO3.  SO running cold seawater through it will dissolve it faster.  Most other impurities will also dissolve at some rate, a few like silica and quartz will not.  Again the rate of dissolving is temperature dependent and how close he seawater is to each compound's saturation at the temperature of the water.