METHODS OF REDUCING CALCITE FORMATION AND SOLUBILIZED METALS FROM AQUEOUS EFFLUENT STREAMS

1 - 75 . (canceled)

76 . A method for treating an aqueous effluent stream containing solubilized forms of selenium, calcium, magnesium, sulfate, and bicarbonate, each present at an initial concentration, the method comprising:

contacting the aqueous effluent stream with a softening composition to provide a softened effluent stream, wherein the softened effluent stream comprises reduced concentrations of calcium, nickel, magnesium and bicarbonate;

reducing the volume of the softened effluent stream to produce a concentrated brine stream comprising selenium and sulfate; and

removing selenium from the concentrated brine stream via selective precipitation of hydrocalumite thereby producing a treated effluent stream having a reduced concentration of selenium.

77 . The method of claim 76 , wherein removing selenium comprises:

contacting the concentrated brine stream with lime and at least one aluminate under conditions effective to precipitate hydrocalumite and incorporate selenium into the hydrocalumite structure, wherein the selective precipitation produces a slurry.

78 . The method of claim 77 , wherein the slurry goes directly to a filter press for solids removal and dewatering.

79 . The method of claim 77 , wherein the aluminate is sodium aluminate.

80 . The method of claim 76 , wherein the softening composition is lime.

81 . The method of claim 80 , wherein the softening composition comprises Ca(OH) 2 .

82 . The method of claim 76 , wherein the aqueous effluent stream has a pH of less than 9.0.

83 . The method of claim 76 , wherein the volume of the softened effluent stream is reduced by nanofiltration prior to selective precipitation of hydrocalumite.

84 . The method of claim 76 , wherein the initial concentration of selenium is at least 100 ppb.

85 . The method of claim 76 , wherein the initial concentration of selenium is at least 200 ppb.

86 . The method of claim 76 , wherein the selenium concentration in the treated effluent stream is less than 25 ppb.

87 . The method of claim 76 , wherein the reduced concentration of selenium is about 0 to about 15 ppb.

88 . The method of claim 76 , further comprising recarbonating the treated effluent stream to reduce the concentration of calcium.

89 . The method of claim 88 , wherein recarbonation is performed by contacting the treated effluent stream with carbon dioxide.

90 . A method for treating an aqueous effluent stream containing solubilized forms of selenium, nickel, calcium, magnesium, sulfate, and bicarbonate, each present at an initial concentration, the method comprising:

contacting the aqueous effluent stream with a softening composition comprising lime to provide a softened effluent stream, wherein the softened effluent stream comprises reduced concentrations of calcium, nickel, magnesium, and bicarbonate;

selectively precipitating hydrocalumite from the softened effluent stream by contacting the softened effluent stream with sodium aluminate and lime to provide a precipitated effluent stream, wherein the precipitated effluent stream comprises reduced concentrations of selenium; and

recarbonating the precipitated effluent stream by contacting with carbon dioxide to provide a recarbonated effluent, wherein the recarbonated effluent comprises a reduced concentration of calcium and a pH of less than 8.0.

91 . The method of claim 90 , wherein the initial concentration of selenium in the aqueous effluent stream is at least 150 ppb.

92 . The method of claim 90 , wherein the precipitated effluent stream comprises less than 10 ppb of solubilized forms of selenium.

93 . The method of claim 90 , wherein the precipitated effluent stream comprises less than 25 ppb of magnesium.

94 . The method of claim 90 , wherein the recarbonated effluent comprises less than 100 ppb of calcium.

95 . The method of claim 90 , wherein the softening composition comprises Ca(OH) 2 .