Process for the treatment of solid alkaline residue comprising calcium, heavy metals and sulphate

Abstract

The invention relates to a process for the treatment of solid alkaline residue comprising calcium, heavy metals and sulphate, the process comprising: a)reacting the solid alkaline residue with carbon dioxide by contacting the solid alkaline residue with a carbon dioxide containing gas to obtain carbonated solid material; and c)washing the carbonated solid material with an aqueous stream to obtain washed solid material and wash water comprising calcium and sulphate and precipitating at least part of the calcium in the wash water as calcium carbonate.

1 - 15 . (canceled) 
     
     
         16 . A process for the treatment of solid alkaline residue comprising calcium, heavy metals and sulphate, the process comprising:
 (a) reacting the solid alkaline residue with carbon dioxide by contacting the solid alkaline residue with a carbon dioxide containing gas to obtain carbonated solid material;   (b) washing the carbonated solid material with an aqueous stream to obtain washed solid material and wash water comprising calcium and sulphate and   (c) precipitating at least part of the calcium in the wash water as calcium carbonate.   
     
     
         17 . The process according to  claim 16 , wherein at least part of the calcium is precipitated in the wash water by adding a carbonate salt to the aqueous stream. 
     
     
         18 . The process according to  claim 16 , wherein at least part of the calcium is precipitated in the wash water by washing the carbonated solid material with an aqueous stream while flowing a stream of carbon dioxide-containing gas through the carbonated solid material. 
     
     
         19 . The process according to  claim 16 , wherein precipitating comprises:
 (i) washing the carbonated solid material with an aqueous stream comprising recycled wash water or water and recycled wash water;   (ii) separating wash water from the carbonated solid material to obtain the washed solid material and the wash water comprising calcium and sulphate;   (iii) supplying the wash water to a separate container;   (iv) adding a carbonate salt or a carbon dioxide-containing gas to the wash water in the separate container to precipitate part of the calcium and to obtain calcium-depleted wash water, wherein, in case a carbon dioxide-containing gas is added to the wash water, the pH of the wash water is adjusted to a value in the range of from 7 to 8 by adding an alkaline compound to the wash water; and   (v) recycling the calcium-depleted wash water to the carbonated solid material as part of the aqueous stream.   
     
     
         20 . The process according to  claim 16  further comprising:
 contacting, for a time period in the range of from 1 week to 12 months, the carbonated solid material obtained in step (a) with a molecular-oxygen containing gas, to obtain mineralised carbonated solid material, 
 wherein in step (c) the carbonated solid material is the mineralised carbonated solid material obtained in step (b). 
 
     
     
         21 . The process according to  claim 20 , wherein the molecular-oxygen containing gas is air. 
     
     
         22 . The process according to  claim 20 , wherein the solid material is kept at a mineralisation temperature in the range of from 20 to 90° C. during the contacting in step (b). 
     
     
         23 . The process according to  claim 22 , wherein the mineralisation temperature is in the range of from 40 to 60° C. 
     
     
         24 . The process according to  claim 22 , wherein no external heat source is used to achieve the mineralisation temperature. 
     
     
         25 . The process according to  claim 20 , wherein the solid material is kept at a moisture content in the range of from 5 to 20 wt % during the contacting in step (b). 
     
     
         26 . The process according to  claim 25 , wherein the moisture content of the solid material is kept in the range of from 8 and 12 wt % during the contacting in step (b). 
     
     
         27 . The process according to  claim 16 , further comprising:
 contacting the washed solid material obtained in step c) with an oxygen-containing gas, for a time period in the range of from 1 week to 12 months.   
     
     
         28 . The process according to  claim 27 , wherein the washed solid material is kept at a temperature in the range of from 20 to 90° C. during the contacting. 
     
     
         29 . The process according to  claim 27 , wherein the washed solid material is kept at a moisture content in the range of from 5 to 20 wt % during the contacting. 
     
     
         30 . The process according to  claim 16 , wherein the solid, alkaline residue is bottom ash from an incineration process.