Tittle : Low Energy Cyclic Method that uses Soluble Metallic Salts in Alkaline Wastes to Sequester Carbon Dioxide

Carbon capture measured on a global scale mandates using starting materials and methods that consumes minimum energy where alkaline wastes and cyclic methods fall on this category. The capability of alkaline waste materials (e.g. C-fly ash, red mud) to sequester C0 ₂ was reported in many references [1,2,3]. However, all literature cited investigated the hydrodynamic and kinetic aspect of the process to justify the possibility of using these wastes in C0 ₂ sequestration. The main byproducts of the cyclic alkaline waste (CAW) carbon capture process are metal carbonates that can be safely returned to earth. The proposed invention uses the following known reaction scheme to sequester C0 ₂ gas, e.g.:

Ca ²⁺ (aq) + C0 ₂ (g) + 20H ^" (aq)→ CaC0 ₃ (s) + H ₂ 0(1)

ENGSL Minerals DMCC filed multiple patents in carbon capture technology where it basically used membrane and ion exchange technologies to manipulate the sequestration of C0 ₂ . The reason for using such advanced technologies is to produce commodity chemicals such as soda ash, sodium hydroxide, and sodium bicarbonate. However, our patent pending process that uses alkaline wastes can operate without the need of producing soda chemicals if the main objective is to sequester C0 ₂ gas. Main advantage gained in C0 ₂ sequestration only is minimum energy and equipment required which in fact makes the CAW process most energy efficient worldwide at ~ 30 KWh/ton C0 ₂ captured. In this we assume that zero energy was involved in the making of alkaline wastes (e.g. C-fly ash, red mud) rendering the pumping units the only energy demanding items. The way to do this is to prepare a fly ash/red mud slurry (or any alkaline waste slurry therein) and a bulk volume of pure water at the start of the process. Water is mixed with the FA/RJvl powder slurry in multiple preparation slurry tanks of TSS = 1% in order to extract the maximum hydroxides. The fly ash slurry stream is then passed to a filter/clarifier bed to obtain a clear stream. In fact, based on the soluble metal content (i.e. Ca , Mg , Fe , Al ) in both the FA and RM matrices the two waste powders can be mixed where % FA > % RM (assuming 1% slurry of RM has a pH > 13) to generate a pH that allows full capture of all C0 ₂ . For example, a typical sample of pH=12.66 can handle metal TDS ~ 900 ppm. The clarifier separates the suspended particulates from the liquid where the processed paste is returned back to earth or marketed while the clear caustic liquid is diverted to a purge carbonator where it is reacted with C0 ₂ in a flue gas stream. In the carbonator the above reaction occurs to form white milky slurry which is treated by a 2 ^nd filter/clarifier. Two streams are generated by the 2 ^nd clarifier where the process stream is cycled to the preparation tank in order to minimize process water usage and energy consumption. In the 2 ^nd stream the carbonate paste is returned to earth or marketed.

The cyclic process can be taken one step further by carefully dosing the system with sodium chloride NaCl as the pH is lowered to approximately 8. Under these conditions sodium bicarbonate (NaHC0 ₃ ) is allowed to form and by virtue of continuous recycling the NaHC0 ₃ gets concentrated until eventually precipitates. In theory, the quantity of NaHC0 ₃ that precipitates is the excess carbonates that are present in the system after precipitating all insoluble carbonates such as CaC0 ₃ . The same procedure might also extract sodium carbonate from the cyclic stream. Various processes are conveniently outlined in the block diagrams next pages followed by sample theoretical analysis on an Excel worksheet.

Scheme I: A facility that emits 100,000 ton/yr (-12 ton/hr) of C0 ₂ gas and produces CaC0 ₃ ,

Scheme II: Do away with the clarifier/filter but the end product is a mixed cake of wet FA/RM paste and calcium carbonate. Same conditions as in scheme I.

Scheme III: A facility that emits 100,000 ton/yr (-12 ton/hr) of C0 ₂ gas and produces NaHC0 ₃ / Na ₂ C0 ₃ as additional byproducts.

References:

1. Uliasz-Bochencz, Alicja; Mokryzcki, Eugeniusz, C0 ₂ sequestration with the use of fly ash from hard coal and lignite combustion". Slovak Geological Magazine, 2009, (Spec. Issue), 19-22. [Journal written in English]

2. Yadav VS, Prasad M, Khan J, Amritphale SS, Singh M, Raju CB, "Sequestration of

carbon dioxide (C02) using red mud" J Hazard Mater. 2010 Apr 15;176(1-3):! 044-50. 4.

3. Danielle Bonenfant, Lynda Kharoune, Sebastien Sauve, Robert Hausler, Patrick Niquette, Murielle Mimeault'and Mourad Kharoune, "C0 ₂ Sequestration by Aqueous Red Mud Carbonation at Ambient Pressure and Temperature", Ind. Eng. Chem. Res., 2008, 47 (20), pp 7617-7622