Fly Ash and Fly Ash Leachate Treatment

Abstract

The present invention is directed to a process of treating fly ash and/or fly ash leachate to immobilize heavy metals contained in such fly ash and/or fly ash leachate, which process comprises treating such fly ash and/or fly ash leachate with a soluble ferrous compound under alkaline conditions. This process may be conducted in the absence of any pH modification, mixing (in the sense of a physical blending with a solid material), drying or heating steps, making it practical for treatment of alkaline fly ash (and other coal combustion by-products) which is currently stored in landfills or wet ash lagoons, particularly fly ash which has been recovered from flue gas streams treated with highly alkaline materials such as trona, bicarbonate or limestone and the like.

What is claimed is: 
     
         1 . A process of treating fly ash and/or fly ash leachate to immobilize heavy metals contained in such fly ash and/or fly ash leachate, which process comprises treating such fly ash and/or fly ash leachate with a soluble ferrous compound under alkaline conditions without a subsequent drying step. 
     
     
         2 . The process of  claim 1  wherein the fly ash is present in a solid landfill. 
     
     
         3 . The process of  claim 1  wherein the fly ash is located in an ash lagoon. 
     
     
         4 . The process of  claim 1  wherein the fly ash was produced employing at least one member from the group consisting of trona, bicarbonate and limestone as a desulfurant. 
     
     
         5 . The process of  claim 4  wherein the fly ash was produced employing trona as a desulfurant. 
     
     
         6 . The process of  claim 1  wherein the fly ash has a pH of 8 or higher. 
     
     
         7 . The process of  claim 6  wherein the fly ash has a pH of 10 or higher. 
     
     
         8 . The process of  claim 1  wherein the soluble ferrous compound is ferrous sulfate or a hydrated form thereof. 
     
     
         9 . The process of  claim 1  wherein the soluble ferrous compound is ferrous chloride or a hydrated form thereof. 
     
     
         10 . The process of  claim 1  wherein such process is conducted in situ. 
     
     
         11 . The process of  claim 1  wherein the heavy metal is selected from the group consisting of selenium, arsenic, vanadium, chromium, cadmium, lead, nickel and mercury. 
     
     
         12 . The process of  claim 11  wherein the heavy metal is selected from the group consisting of selenium, arsenic, vanadium, and chromium. 
     
     
         13 . The process of  claim 12  wherein the heavy metal is selenium. 
     
     
         14 . The process of  claim 12  wherein the heavy metal is arsenic. 
     
     
         15 . The process of  claim 1  wherein fly ash leachate is treated and between 0.5 grams of Fe(II) per liter of leachate and 15 grams of Fe(II) per liter of leachate is employed. 
     
     
         16 . The process of  claim 1  wherein fly ash is treated and between 0.1 weight percent and 15 weight percent Fe(II) is employed, based upon the weight of the fly ash to be treated.