Method for removing heavy metals from aqueous liquids

Claim 1

A method for processing an aqueous feed liquid to precipitate at least one metal sulfide in a form to make said sulfide subsequently removable from said stream by settling and filtration, comprising the steps of (a) circulating within a loop a volume of an aqueous liquid containing a soluble salt of the metal to be removed and establishing within said loop in order of liquid flow at least one mixing zone, a controlled precipitation initiating zone, a crystal growing zone, and a crystal settling zone; (b) introducing into said loop upstream from said mixing zone aqueous feed liquid to be processed, said aqueous liquid containing H 2 S, in excess of that required to react with said metal, dissolved therein and having a pH less than that at which the sulfide of said metal precipitates; (c) introducing into said mixing zone an aqueous pH-adjusting liquid in a quantity sufficient to raise the pH of said liquid in said loop to a point between that at which said liquid becomes slightly supersaturated with respect to said metal sulfide and that at which precipitation of said metal sulfide is initiated; (d) maintaining the degree of supersaturation within said controlled precipitation initiating and crystal growing zones in the metastable condition whereby the growth rate of metal sulfide crystals remains greater than under uncontrolled conditions vis-a-vis the nucleation rate throughout essentially the entire precipitation of sai metal sulfide and said metal sulfide formed is of a particle size distribution which permits it to collect in said crystal settling zone and to provide aqueous liquid for recirculation in said loop; and (e) drawing off from said loop the the metal sulfide magma formed in said crystal settling zone; the volume flow of said liquid in said loop being essentially equivalent to the product of volume flow rate of said aqueous liquid introduced into said loop and the residence time of a hypothetical volume of said liquid introduced into said loop.

Claim 2

A method for processing an aqueous feed liquid to precipitate at least one metal sulfide in a form to make said sulfide subsequently removable from said stream by settling and filtration, comprising the steps of (a) circulating within a loop a volume of an aqueous liquid containing a soluble salt of the metal to be removed and establishing within said loop in order of liquid flow at least one mixing zone, a controlled precipitation initiating zone, a crystal growing zone, and a crystal settling zone; (b) introducing into said loop upstream from said mixing zone aqueous feed liquid to be processed, said aqueous liquid containing H 2 S, in excess of that required to react with said metal, dissolved therein and having a pH less than that at which the sulfide of said metal precipitates; (c) introducing into said mixing zone an aqueous pH-adjusting liquid in a quantity sufficient to raise the pH of said liquid in said loop to a point between that at which said liquid becomes slightly supersaturated with respect to said metal sulfide and that at which precipitation of said metal sulfide is initiated; (d) maintaining the degree of supersaturation within said controlled precipitation initiating and crystal growing zones in the metastable condition whereby the growth rate of metal sulfide crystals remains greater than under uncontrolled conditions vis-a-vis the nucleation rate throughout essentially the entire precipitation of sai metal sulfide and said metal sulfide formed is of a particle size distribution which permits it to collect in said crystal settling zone and to provide aqueous liquid for recirculation in said loop; and (e) drawing off from said loop the the metal sulfide magma formed in said crystal settling zone; the volume flow of said liquid in said loop being essentially equivalent to the product of volume flow rate of said aqueous liquid introduced into said loop and the residence time of a hypothetical volume of said liquid introduced into said loop.

Claim 6

A method for removing from an aqueous feed liquid at least one heavy metal present therein as a soluble salt by reaction with H 2 S to form an insoluble metal sulfide, comprising the steps of (a) dissolving in said aqueous feed liquid a quantity of H 2 S in excess of that required to react with said heavy metal, the pH of said feed liquid being below that at which the dissolution of said H 2 S will cause precipitation; (b) providing a circulating loop of said aqueous liquid and establishing within said loop in order of liquid flow at least one mixing zone, a controlled precipitation initiating zone, a crystal growing zone, and a crystal settling zone; (c) introducing into said loop upstream from said mixing zone, said aqueous liquid containing H 2 S dissolved therein; (d) introducing into said mixing zone an aqueous pH adjusting liquid in a quantity sufficient to raise the pH of said liquid in said loop to a point between that at which said liquid becomes slightly supersaturated with respect to said metal sulfide and that at which precipitation of said metal sulfide is initiated; (e) maintaining the degree of supersaturation within the controlled precipitation initiating and crystal growing zones in the metastable condition whereby the growth rate of metal sulfide crystals remains greater than under uncontrolled conditions vis-a-vis the nucleation rate throughout essentially the entire precipitation of said metal sulfide and the metal sulfide formed is of a particle size distribution which permits it to collect in said crystal settling zone and to provide aqueous liquid for recirculation in said loop; (f) drawing from said loop the metal sulfide magma formed in said crystal settling zone; and (g) removing said metal sulfide from said magma by clarifying and filtration to provide an aqueous liquid from which said heavy metal is removed.

Claim 7

A method for removing from an aqueous feed liquid at least one heavy metal present therein as a soluble salt by reaction with H 2 S to form an insoluble metal sulfide, comprising the steps of (a) dissolving in said aqueous feed liquid a quantity of H 2 S in excess of that required to react with said heavy metal, the pH of said feed liquid being below that at which the dissolution of said H 2 S will cause precipitation; (b) providing a circulating loop of said aqueous liquid and establishing within said loop in order of liquid flow at least one mixing zone, a controlled precipitation initiating zone, a crystal growing zone, and a crystal settling zone; (c) introducing into said loop upstream from said mixing zone, said aqueous liquid containing H 2 S dissolved therein; (d) introducing into said mixing zone an aqueous pH adjusting liquid in a quantity sufficient to raise the pH of said liquid in said loop to a point between that at which said liquid becomes slightly supersaturated with respect to said metal sulfide and that at which precipitation of said metal sulfide is initiated; (e) maintaining the degree of supersaturation within the controlled precipitation initiating and crystal growing zones in the metastable condition whereby the growth rate of metal sulfide crystals remains greater than under uncontrolled conditions vis-a-vis the nucleation rate throughout essentially the entire precipitation of said metal sulfide and the metal sulfide formed is of a particle size distribution which permits it to collect in said crystal settling zone and to provide aqueous liquid for recirculation in said loop; (f) drawing from said loop the metal sulfide magma formed in said crystal settling zone; and (g) removing said metal sulfide from said magma by clarifying and filtration to provide an aqueous liquid from which said heavy metal is removed.