I assume you want to remove sand from a mixture (say sand and salt). Sand is removed by using filtration, since sand is insoluble in water. So, if you are given a mixture containing water soluble substances (such as salt or sugar) and sand (water insoluble) and your objective is to separate them out. Mix everything in water. Sand, being insoluble, will not dissolve in water, while salt will (we can aid it by heating the water and gently stirring). Once the salt is completely dissolved in water, we can filter the solution through a filter paper. Sand, being water-insoluble and because of its larger size (as compared to the filter's pore size), will be retained on the filter paper. We can allow the filter to air-dry or put it in a laboratory oven to dry it faster. Once the filter paper is completely dry, all the sand can be removed from it. (We can also remove all the salt from water by simply boiling it.).
Sand is not a liquid it is a bonding of particles which are few in number to be attached together so some molecules are held together tightly.It is insoluble in liquid and hence when we mix sand,salt and water we can see salt and water have completely dissolved but sand is circulating around the water and finally settles at the bottom.A filter paper is used to filter away the undissolved solutes from a solvent.The filtrate the sand cannot pass since the filter paper allows only small particles to pass and sand being a larger molecule in size cannot pass.The residue salt and water do pass easily because salt is dissolved in water.Now to obtain pure water we can use the process of distillation where the water is heated till it evaporates.