Marble: acid dissolution

The dissolution of carbonates by acid is an undesired result of acid rain, which has damaged the appearance of many historic marble and limestone monuments (Fig. 11.19 marble and limestone are forms of calcium carbonate). 

FIGURE 44 Weathering. A weathered sandstone column. Calcite (composed of calcium carbonate) is dissolved by rain and groundwater (see Textbox 73). When stone in which calcite is a main component as, for example, sandstone, limestone, and marble, is in contact with water for long periods of time, it is weathered and partly or entirely dissolved. Pollutants such as sulfur dioxide are fundamental in accelerating the weathering and dissolution process. When sulfur dioxide, for example, dissolves in rainwater, it forms sulfuric acid, a strong acid that, at ambient temperatures, rapidly dissolves calcium carbonate. 

Schuster, P. F., M. M. Reddy, and S. I. Sherwood (1991), A quantitative field study of the role of acid rain and sulfur dioxide in marble dissolution, La Conservation des Monuments dans le Bassin Mediterranean, Proc. 2nd Int. Symp., Geneve. 

Arsenious oxide exhibits considerable catalytic activity, which may act either positively or negatively. The effect on many oxidation and reduction reactions has been mentioned above. Other examples are the increase in the rate of dissolution of zinc by dilute acids and the retardation of the dissolution of marble. In the latter case a concentration of 0-005N As303 reduces the velocity constant for the dissolution of marble in 0-1N HC1 by 12 per cent.5... 

The effect of pH on the solubility of CaC03 has important environmental consequences. For instance, the formation of limestone caves, such as Mammoth Cave in Kentucky, is due to the slow dissolution of limestone (CaC03) in the slightly acidic natural water of underground streams. Marble, another form of CaC03, also dissolves in acid, which accounts for the deterioration of marble monuments on exposure to acid rain (Interlude, pages 650-651). 

Clearly, there are real differences in ki between experiments. The highest value of ki is estimated from the data of Weyl (9 )y who directed a jet of CO2-saturated water (pH = 3.9) onto the surface of calcite. Weyl found that the rate of solution varied with the jet velocity. His rates imply that kj varies from 0.11 to 0.23 when velocity of the jet increases from 18 to 35 m sec The smallest value of k (.0073) is derived from the data of Tomlnaga et al. (10). These authors rotated a disk of marble in HCl solutions (0.1750 - 0.5317N) at 485 rpm. Rate of dissolution was followed by the volume of CO2 evolved. After an initial period for saturation of the acid with CO2, rate of gas evolved becomes linear in the cumulative amount of CO2 produced. Because the acid concentration decreased as calcite dissolved, we extrapolated the observed linear relation in CO2 production back to the initial condition to estimate Initial rates under known acid concentrations. Correction to pH via the Davies equation leads to the rates shown for these authors in Figure 6. 

The rate of dissolution of marble (CaC03) in hydrochloric acid is an example of a chemically controlled reaction. The rate can be measured from the evolution of carbon dioxide. Palmer and Clark found that the rate of dissolution of silica in hydrofluoric acid was proportional to surface area and acid concentration. The rate of reaction was measured by noting the increase in conductivity of the solution... 

As first example we consider the dissolution of limestone or marble in hydrochloric acid (Fig. 4). 

Fig. 4 Dissolution of marble in hydrochloric acid, if hydrochloric acid, an aqueous solution of hydrogen chloride, HCl, is poured over marble, foam develops that contains carbon dioxide. HCl is a strong acid and is entirely dissociated into hydrogen and chloride ions, H+ and Cl . The H+ ions are responsible for the reaction while the CT ions remain more or less inactive.

Reddy, M. M. Sherwood, S. I. Limestone and Marble Dissolution by Acid Rain. In this book. 

In this paper, we describe an onsite weathering experiment designed to identify acid-rain increased dissolution of carbonate rock. This experiment is based on the measurement of the change in rainfall-runoff composition from the interaction of a rock surface with incident acid rain 2. The experiment involves conducting long-term exposures of two commercially and culturally important calcium carbonate dimension stones (i.e., Indiana Limestone (commercial name for Salem Limestone) and Vermont Marble (commercial name for Shelburne Marble)) (3-5). This technique appears to give a direct measurement of the chemical dissolution of carbonate rock from the combined reactions of wet and dry deposition. Preliminary results from the initial months of onsite operation are presented to illustrate the technique. 

Dissolution by Acid Rain. The dissolution of limestone and marble by acid rain may be written as ... 

Reddy, M. Sherwood, S. Doe, B. "Limestone and Marble Dissolution by Acid Rain" to be sumitted to Proc. 5th Int. Cong, on Deterioration and Conservation of Stone, Lausanne, Switzerland, Sept. 1985. 

Dissolution of marble in hydrochloric acid. If a few pieces of marble are put in hydrochloric acid, a strong effervescence of carbon dioxide can be observed. 

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