Carbonation of wollastonite under hydrothermal alkali condition

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Other Title
  • アルカリ性熱水環境における珪灰石の炭酸塩化
  • アルカリ性熱水環境における珪灰石の炭酸塩化 : 炭酸ナトリウム溶液を用いた実験的研究
  • アルカリセイ ネッスイ カンキョウ ニ オケル ケイカイセキ ノ タンサン エンカ : タンサン ナトリウム ヨウエキ オ モチイタ ジッケンテキ ケンキュウ
  • an experimental approach with sodium carbonate solution
  • 炭酸ナトリウム溶液を用いた実験的研究

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Abstract

In order to understand the processes and mechanism for carbonation of wollastonite under hydrothermal alkali condition, chemical reaction of wollastonite with sodium carbonate solution was experimentally examined. In the experiment, crashed and sieved wollastonite grains between 1.00 and 1.18 mm in diameter were sealed in the polypropylene bottle with sodium carbonate solution, and left for fixed duration in time. A series of experiment with 1/450 mineral/solution weight ratio was carried out with changing temperature (90∼170°C), concentration of sodium carbonate solution (0.01, 0.1 and 1 mol/l), and reaction time (1∼2184 hours). The run products were filtered by 0.20 mm membrane filters, and the filtrated solution and residual solid were analyzed.<br>In the residual solid for all runs, the one and only identified reaction product was calcite. Calcite grains grew on surfaces of initial wollastonite grains. The size of calcite grains increases with the increase of reaction time, suggesting Ostwald ripening. Residual silica layers cannot be recognized both on surfaces and in sections. Amount of calcite increases with the increase of temperature, initial Na2CO3 concentration and reaction time, in the range of 89.5 % calcite/total Ca (150°C-1 mol/l initial Na2CO3) and 9.3% (90°C-0.01 mol/l) for 2184 hours. Whereas Ca concentration in solution was undetectable, Si concentration increased with the increase of temperature, initial Na2CO3 concentration and reaction time. The stoichiometric relationship between the Si concentration in solution and amount of calcite indicates that dissolution of wollastonite proceeds congruently. Dissolution rate of Si from wollastonite for 24 hours increases with the increase of temperature and initial Na2CO3 concentration, in the range of 4.05 x 10-8 mol·s-1·m-2 for the condition of initial Na2CO3 0.01 mol/l-90°C and 7.49 x 10-7 mol·s-1·m-2 for the condition of initial Na2CO3 1 mol/l-170°C. The rate of calcite formation for 24 hours is slightly higher than the dissolution rate of Si from wollastonite, suggesting that the dissolution rate of Si from wollastonite is slower than that of Ca and the rate limiting step for wollastonite carbonation is dissolution. Thus, carbonation of wollastonite proceeds easily under hydrothermal alkali condition.

Journal

  • Shigen-Chishitsu

    Shigen-Chishitsu 62 (2), 139-149, 2012

    The Society of Resource Geology

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