The present invention provides an integrated process for the recovery of sulphate of potash (SOP), ammonium sulphate and surface modified magnesium hydroxide and/or magnesium oxide utilizing kainite mixed salt and ammonia as the only consumable raw materials. The process involves treating kainite mixed salt with water to obtain solid schoenite and a schoenite end liquor. The latter is desulphated using CaCl2 generated in the process itself and thereafter evaporated to obtain carnallite crystals from which KCl is recovered while the liquor rich in MgCl2 serves as a source of MgCL. The gypsum produced during desulphatation is reacted with aqueous ammonia and CO2 to produce ammonium sulphate and calcium carbonate. The calcium carbonate so obtained is then calcined to obtained CaO and CO2. The CaO is then slaked in decarbonated water and reacted with the MgCl2-rich liquor generated above to produce slurry of Mg(OH)2 in aqueous CaCl2. To this surface modifying agent is added under hot condition and, after cooling, the slurry is more easily filterable and yields surface modified Mg(OH)2. The filtrate rich in CaCl2 is then recycled for desulphatation process above. The solid surface modified Mg(OH)2 is then calcined to produced MgO or used as such in appropriate applications. The schoenite and KCl are reacted to produce SOP in solid form while the liquor is recycled in the schoenite production step.