The notion of storing CO2in minerals isn’t new. Plans to capture the gas from the air or power plant exhaust often call for injecting it into underground rock formations that, like mine waste, react to form carbonates. And certain rocks naturally capture CO2in a process known as weathering. Vast ridges of a mineral called peridotite mineralize CO2fromthe air, forming white veins resembling marbling in steak. Mine wastes behave the same way.

將二氧化碳礦化封存的概念并不稀奇。人為手段通常的思路是：捕集大氣中彌漫的二氧化碳或電廠排放的廢氣，將之注入可發(fā)生化學(xué)反應(yīng)的地下巖層，這些巖層和礦山廢料一樣，會與二氧化碳反應(yīng)形成碳酸鹽礦物。同時，某些巖石能自然吸收二氧化碳，這一過程被稱為“風(fēng)化”。比如，橄欖巖能將空氣中的二氧化碳礦化成白色礦脈，覆在其巨大山脊上形如牛排上的雪花紋。礦山廢料對二氧化碳的固化方式亦是如此。

Still, weathering is slow, and most alkaline wastes wind up either buried or submerged in ponds, and thus aren’t exposed to air. At Gahcho Kué, Dipple and his students tested a way to speed up the process. The waste soaked up CO2for as long as 44 hours, they found, converting it into minerals. The newly made magnesium carbonate minerals acted like glue, solidifying the previously free-flowing tailings, much like sand turned to sandstone. Most important, the waste took up CO2200 times faster than it did through natural weathering, Dipple says.

不過，自然的風(fēng)化過程是緩慢的，而且大多數(shù)堿性廢料都淹埋在了池塘里，因而無法接觸空氣并吸收二氧化碳。在加拿大的Gahcho Kué鉆石礦場里，Dipple和他的學(xué)生們嘗試加速風(fēng)化這一過程。經(jīng)過實驗他們發(fā)現(xiàn)，在僅長44個小時的吸收和礦化后，廢料將二氧化碳轉(zhuǎn)變成了礦物質(zhì)。新形成的碳酸鎂礦物如同膠水，將原先隨處散落的尾礦顆粒固著，很像沙子形成砂巖的過程。Dipple說，利用廢料吸收二氧化碳的速度比自然風(fēng)化快200倍，這一點非常重要。

CO2mineralization could help remediate environmental problems that mining creates, such as the release of heavy metals from pulverized rock. Earlier this year in Economic Geology, Wilson and her colleagues reported that techniques that accelerate weathering, such as adding acid, effectively trap heavy metals inside newly formed carbonate minerals, keeping them out of groundwater. Other teams have shown that the carbonates can also trap hazardous residual asbestos fibers in chrysotile mine tailings. “You can lock away just about anything,” Wilson says.

二氧化碳的礦化還可以緩解礦采中的環(huán)境問題，比如解決粉碎巖石時釋放的重金屬。在年初出版的《經(jīng)濟(jì)地質(zhì)學(xué)》中，Wilson與同事報告了加速風(fēng)化的一些技術(shù)，如通過添加酸能有效將重金屬封存在新形成的碳酸鹽礦物中，從而使其遠(yuǎn)離地下水。也有一些研究小組發(fā)現(xiàn)，碳酸鹽礦物能封存溫石棉尾礦中殘留的有害石棉纖維。Wilson認(rèn)為，“利用二氧化碳的礦化能儲存幾乎任何有害物質(zhì)?！?/span>

Other industrial wastes, such as red mud from aluminum production and “slags” leftover from making steel and iron, also harbor plenty of chemical reactivity to bind and store CO2. However, according to the National Academy of Sciences (NAS), fully carbonating these wastes could require building costly plants to speed the reactions.

其它的工業(yè)廢料，諸如生產(chǎn)鋁的過程中出現(xiàn)的赤泥，鍛鋼和煉鐵后殘余的礦渣，都能與二氧化碳發(fā)生大量的化學(xué)反應(yīng)并結(jié)合成礦物質(zhì)將之封存。不過，根據(jù)美國國家科學(xué)院（NAS）的說法，將這些工業(yè)廢料完全碳酸鹽化則需要耗巨資建廠來加速反應(yīng)過程。

In another environmental plus, the NAS panel said, carbonated wastes of all kinds could serve as raw material for concrete and road aggregate. The report noted that replacing 10% of building materials with carbonated minerals could reduce CO2emissions by 1.6 GTs per year by lowering emissions from cement production. Numerous companies around the globe have already jumped into the field to make and sell the new materials.

該學(xué)院專家組還提到二氧化碳礦化的另一環(huán)境優(yōu)勢，碳酸鹽化的各種工業(yè)廢料可作為原材料用于制作混凝土和修路用骨料。報告指出，用碳酸鹽礦物替代10%的水泥建筑材料，每年能減少1.6 GTs的碳排放。全球已有不少公司涉足該領(lǐng)域在制造并銷售這種新材料。

選編自Science, September 4th 2020