Article pubs.acs.org/IECR
CO2 Mineralization of Activated K‑Feldspar + CaCl2 Slag To Fix Carbon and Produce Soluble Potash Salt Longpo Ye,† Hairong Yue,† Yufei Wang,‡ Haoyi Sheng,† Bo Yuan,† Li Lv,† Chun Li,† Bin Liang,*,† Jiahua Zhu,† and Heping Xie‡ †
Multi-Phases Mass Transfer and Reaction Engineering Laboratory, College of Chemical Engineering, Sichuan University, Chengdu 610065, China ‡ Center of CCUS and CO2 Mineralization and Utilization, Sichuan University, Chengdu 610065, China S Supporting Information *
ABSTRACT: We report an alternative technology for the mineralization of CO2 and production of soluble potash fertilizer via thermal activation of the insoluble K-feldspar with industrial waste of CaCl2 with lower energy consumption since the activation temperature was about 800−900 °C compared with the conventional temperature of 1300 °C. A remarkable K-extraction and CO2 mineralization ratio could be obtained at an appropriate activation temperature and content of additive CaCl2, which possessed the exchange of skeletal K+ with dissociative Ca2+ to form soluble K+ species, the collapse of K-feldspar framework, and the formation of intermediates (e.g., anorthite, pseudowollastonite, and wollastonite) to react with CO2. Characterization results (e.g., XRD, EDS, and SEM) indicated that pseudowollastonite and wollastonite were the major species to fix CO2. Moreover, the reaction principles of the K-extraction and CO2 mineralization were discussed, and a possible mechanism was proposed.
1. INTRODUCTION Carbon dioxide (CO2) is the primary greenhouse gas emitted through human activities.1 According to the IPCC Fifth
researchers have reported the mineralization of CO2 with natural ores, such as serpentine and olivine.29−32 Balucan and Dlugogorski studied the thermal activation of serpentinites and weak acid processing of wollastonite for mineralization of CO2, and they also presented fuel cost estimates based on a practical heat activation strategy for serpentinites.33−38 Although the CO2 mineral sequestration has the recognized and welldocumented advantages, e.g., very large capacity, no poststorage monitoring needed, and exothermic overall process chemistry, it is somewhat expensive and not economically favorable.6,39−41 K-feldspar is an insoluble mineral of potassium, and the potassium cannot be directly absorbed by plants. As there is a shortage of soluble potassium resource in some countries, many efforts have been made to produce potassium fertilizer from Kfeldspar.42−45 In the conventional processes for the use of Kfeldspar, the ore was roasted at an elevated temperature (e.g., >1300 °C) to convert K components into soluble salts.44,46 The roasted ore was then extracted with hot water for the leach of potassium. However, these are energy consumption processes and not economically practicable. An alternative CCUS (carbon capture, utilization, and storage) method was proposed to fix CO2 in the process of potassium extraction from insoluble K-feldspar.47 This process is an integrated technology consisting of the activation of Kfeldspar with calcium chloride hexahydrate at 800−850 °C and the mineralization of CO2 in the suspension residue of the leached slag. The additivecalcium chlorideis a waste deposited in soda-ash production of Solvay method. It is a large environmental challenge for more than 10 million tons of
Scheme 1. Scheme of Overall Experimental Process in This Work
Assessment Report of Climate Change 2013 (AR5), in 2011 the concentration of CO2 was 391 ppm and exceeded the preindustrial level by about 40%. It is estimated that global temperature rise will reach a maximum of 2.6−4.8 °C during the 2081−2100 period compared with 1986−2005.2 In 2012, global CO2 emissions increased by 1.4% and reached a record of 31.6 billion tons (IEA, 2012). Technologies of CO2 capture and storage (CCS) have been intensively investigated in the past couple of decades,3−13 including physical storage, biological fixation, and chemical fixation.14−22 The current CCS methods are still far from commercialization due to the high cost and high energy consumption.23 The storage of CO2 may induce risks of leakage, contamination of underground water, or geologic disasters.23−27 CO2 mineralization is one of the promising methods for chemical fixation of CO2 via reaction with alkaline earth oxides to form carbonates. It could store CO2 stably for thousands of years. Alkaline-earth oxides, such as magnesium oxide (MgO) and calcium oxide (CaO), exist in large amounts and high concentrations in the natural silicate minerals.28 Many © 2014 American Chemical Society
Received: Revised: Accepted: Published: 10557
March 7, 2014 June 1, 2014 June 10, 2014 June 10, 2014 dx.doi.org/10.1021/ie500992y | Ind. Eng. Chem. Res. 2014, 53, 10557−10565
Industrial & Engineering Chemistry Research
Article
Figure 1. Compositional analysis of the dried K-feldspar ore.
Table 1. Elemental Composition of K-Feldspar Ore element (as oxide) mass percentage (%)
K2O 8.29
Al2O3 18.25
SiO2 58.52
deposit per year. Therefore, this new process is also environmentally benign due to the reduction of CaCl2. Compared with the reported high-temperature thermal activation process for the utilization of potassium, K-feldspar activated with CaCl2 at about 900 °C in this process is energy saving and reduces the emission of CO2 by mineralization. According to a report of the U.S. Geological Survey, estimated world potash mine reserves are about 95 billion tons of equivalent K2O in 2012. Substantial reserves of K-feldspar ore make it a promising way to store CO2 permanently on an industrial scale. Although most of the potassium fertilizer is, nowadays, produced from soluble K-resources over the world, the K-feldspar is a potential K-resource in the countries and regions lacking soluble K-resources. The scheme of experimental procedure is shown in Scheme 1. K-feldspar was first activated at a certain temperature (e.g., 800−900 °C) to exchange K+ with Ca2+ ions of anhydrous calcium chloride. The activated slag was leached with hot deionized water (ca. 80 °C) to extract potassium, and then CO2 was bubbled in the suspension of the residue for the mineralization of CO2. The fundamental reactions and operating parameters were systematically investigated to obtain the K-extraction ratio and the CO2 mineralization ratio of the filtration cake. The solid phases in both activation and mineralization steps were characterized, and the reaction mechanisms were also discussed based on the experimental and characterization results.
CaO 1.78
Na2O 2.46
Fe2O3 2.23
others 8.47
Figure 2. K-extraction ratios for three parallel experiments.
2. MATERIALS AND METHODS Materials. K-feldspar ore was mined from Shanxi Shangluo, China. The ore was first dried at 120 °C for 24 h to dehydrate. Calcium chloride (AR) was ground to
