which of the following salt solution Caco3, CaCl2, CA(OH)2 and CH3COONa
(0.1M eoch) will have the lowest pH values?
Answers
Explanation:
1. Introduction
Addressing the continuous rise of atmospheric carbon dioxide levels has become
a focus of global efforts. Research in carbon capture and storage (CCS) has increased
substantially in the last decade [1, 2]. Current carbon storage research has been primarily
concentrated on sequestering CO2 in underground geologic formations such as saline
aquifers, depleted oil and gas fields, and unmineable coal seams. These methods of
geologic sequestration have the advantage of being relatively low cost when separated
from CO2 capture, separation, and transportation. However, potential issues associated
with sequestration in geologic formations include: permanence, long-term monitoring,
and verification, with many unknown effects and potential risks still to be determined [3,
4]. An alternative to conventional geologic sequestration is carbon mineralization, where
CO2 is reacted with metal cations such as magnesium, calcium, and iron to form
carbonate minerals. Mineralization methods can be broadly divided into two categories:
in situ and ex situ. In situ mineralization, or mineral trapping, is a component of geologic
sequestration, in which a portion of the injected CO2 reacts with the alkaline minerals
present in the target formation to form solid carbonate species. In ex situ mineralization,
the carbonation reaction occurs above ground, within a separate reactor or industrial
process. Mineral CO2 sequestration seeks to mimic the natural weathering process [5] in
which calcium or magnesium silicates are transformed into carbonates via reaction with
CO2 gas and/or aqueous CO2
(Ca,Mg)SiO3 (s) + CO2 (g) (Ca,Mg)CO3 (s) + SiO2 (s) … (1)
Original development of ex situ CO2 mineralization of calcium and magnesiumbearing silicate minerals occurred at Los Alamos National Laboratory in the mid to late
1990’s [6]. Work in this area continued to evolve at the National Energy Technology
Laboratory (NETL), where the direct aqueous mineralization method was advanced [7].
Over the course of the last decade the amount of research being performed in this area
has increased and spread worldwide. Several comprehensive reviews have been
published on both ex situ and in situ CO2 mineralization, the most recent of which were
prepared in Europe [8, 9]. Prior to these, Huijgen and Comans published a very thorough
review in 2003 [10], and followed it up with an update in 2005 [11]. Part of the
Intergovernmental Panel on Climate Change (IPCC) report from 2005 included an
extensive summary of CO2 mineralization [1]. In 2008, a number of reviews were
published by others [12, 13].
The IPCC report [1] suggested that the “highly verifiable and unquestionably
permanent” nature of the mineral carbonation storage mechanism is likely to lead to its
greater public acceptance. In situ mineralization or mineral trapping has been examined
as a potentially stable and cost-effective storage mechanism, but most researchers agree
that the fraction of CO2 mineralized under reservoir conditions will be minor in the first
few hundred years. However, less research has been done to evaluate the geochemical
interaction between CO2 with shale and other formations expected to act as natural seals
for the injected CO2. In some cases, these formations may be permeable to/or reactive
with CO2, and could be either mineralization candidates or leakage pathways. A
fundamental investigation of the reactivity of clays and/or shale with CO2 would help
define their roles in geologic sequestration. Overall, the in situ mineralization technolog