Abstract: A lime-treatment method is disclosed to neutralize acidic waters containing heavy metals and sulphate and precipitate the metals as hydroxides along with calcium sulphate solids which are called sludge. The method comprises neutralizing the water in two reactors, the pH of the first reactor being increased to 4-4.5 using a predetermined amount of recycled sludge to precipitate only ferric hydroxides whereas other metal hydroxides coming from the recycled sludge are dissolved, the pH of the second reactor being increased to 9-10 using a mixture of lime and a small amount of the sludge recycled to the first reactor; feeding the ferric hydroxides precipitated in the first reactor to the second reactor to act as nuclei in the second reactor to promote crystallization; and introducing air into the second reactor to oxidize ferrous iron to less soluble ferric iron which results in formation of a more stable sludge compared to ferrous sludge.

Abstract: Gold ions are removed from aqueous solution or suspension by treatment of aqueous material with biomass derived from the genus Sargassum (e.g.: Sargassum natans), a brown sea-water alga. The process can be utilized to remove gold from industrial or natural waters.