4.2 Water

• Dispersed clay particles are too fine to be removed by filtration. They are suspended in water due to the overall negative charge of the aluminosilicate, creating repulsive forces between each other. Thus, highly charged cations such as Al3+ and polymers can attract the negatively charged clay particles to neutralise the charge. By neutralising the charges, the clay particles can come together and form solid flocs, which can be settled down and be removed through filtration. 
• Surfactants are link b/w polar and nonpolar substance. Have ionic hydrophilic carboxylate head + long hydrophobic non-polar hydrocarbon chain. The carboxylate ion forms ion-dipole with polar water molecules. The non-polar hydrocarbon can interact with nonpolar triglycerides via dispersion forces. Thus, the hydrophobic tails embedded in triglycerides with ionic carboxylate heads interacting with water - micelle. Due to the - charged surface of micelle, they dispersed due to repulsion forces. Agitation increases their ability to encapsulate other oil/grease and lift them and wash them away. 
• Acidic conditions cause the carboxylate ions to gain a proton and convert to carboxylic acids, lacking the ionic charge to repel micelles from each other, thus not maintaining their structure.

  Hard water ions such as Ca2+ and Mg2+ can react with the carboxylate ions to form insoluble salts, leading to the formation of scum instead of micelles. Hence, this lowers the surfactant molecules available to form micelles.
• Hard water is water with a high concentration of dissolved ions such as magnesium and calcium ions, producing scum from the insoluble salts made from these ions. 

  Thus, open, porous zeolite molecules can be added so that cation exchange occurs to remove the calcium and magnesium ions with sodium ions. However, when zeolite has run out of space and sodium ions for cation exchange to occur, flushing a concentration solution of sodium ions will remove the bounded Ca2+ and Mg2+. 
• In reverse osmosis, pressure is added to force the saline water through a semipermeable membrane against the osmotic pressure. This allows water molecules to go through but not the majority of dissolved salts, organic matter and bacteria, leading to potable water.
• Desalination via reverse osmosis requires high electrical energy to generate the high pressure needed to force the saline water through the semipermeable membrane, increasing costs.

  Furthermore a waste product of brine is left, which is a very concentrated salt solution, in which dumping back into the ocean damages marine life’s organisms and ecosystems due to the sudden change in salinity. 
• Desalination via thermal processes utilises lots of energy for its heating, increasing production costs. If this heat energy is from the burning fossil fuels, CO2 as a GHG can be emitted..
• Cl2 + H2O -> HOCl + H+ + Cl-

  This equilibrium reaction is used to disinfect and remove bacteria from water. It is optimal to maximise the HOCl concentration as it is the best oxidising agent to remove bacteria.