a) What are the key factors that determine the degree of success in removing of heavy metal ions from wastewater? b) Write the chemical equations that show the best choice of chemical agents added for precipitation of heavy metal ions: Pb, Hg, Zn c) Why hexavalent chromium ions must be first reduced chemically into trivalent chromium ions before chemical precipitation as hydroxide, Cr(OH)3. Give two suitable reducing reagents used in practice. d) Why ferrous ions must be oxidized to ferric ions before iron removal from wastewater as hydroxide, Fe(OH),. Is it possible to use atmospheric oxygen for iron oxidation? e) Cyanide ions exist with heavy metal ions in wastewater from electroplating industry because metal cyanide salts are used. List the steps used in converting the CN-toxic ions into non-hazardous materials. f) In many advanced oxidation processes used to destruct and remove non-biodegradable organics (COD or TOC) in wastewater, ......... and .............. chemical reagents are used with or without ultraviolet light (UV) to produce hydroxyl radical (OH.), which is a powerful species in attacking complex organic compounds. g) What are the stages of hazardous chemical sludge handling and disposal? h) What is the main difference between chemical oxidation and electrochemical oxidation?