Limestone with acids, reaction rates

Temperature. Acid reaction rate increases with temperature. At about 150°F, the reaction rate of HCl and limestone is about twice that at SOT. The reaction rate of HCl in limestone is faster than in dolomite up to about 250°F (or somewhat less). At higher temperatures, the rates of reaction in limestone and dolomite are equally fast. 

Neutralization Acidic or basic wastewaters must be neutrahzed prior to discharge. If an industry produces both acidic and basic wastes, these wastes may be mixed together at the proper rates to obtain neutral pH levels. Equahzation basins can be used as neutralization basins. When separate chemical neutralization is required, sodium hydroxide is the easiest base material to handle in a hquid form and can be used at various concentrations for in-line neutralization with a minimum of equipment. Yet, lime remains the most widely used base for acid neutr zation. Limestone is used when reaction rates are slow and considerable time is available for reaction. Siilfuric acid is the primary acid used to neutralize high-pH wastewaters unless calcium smfate might be precipitated as a resmt of the neutralization reaction. Hydrochloric acid can be used for neutrahzation of basic wastes if sulfuric acid is not acceptable. For very weak basic waste-waters carbon dioxide can be adequate for neutralization. 

Retarded acids are primarily applicable to sandstone acidizing. Fluoroboric acid slowly hydrolyzes to form the more reactive hydrofluoric acid (109,110). The time required for this hydrolysis process may enable deeper penetration of the HF into the formation although one report contradicts these findings (111). Na TiF and similar salts also slowly generate HF in acid media (112). Phosphorous acid addition to hydrochloric acid has been used to reduce the HC1 reaction rate with limestone (113). 

What apparatus would you use to measure the rate of reaction of limestone with dilute hydrochloric acid by measuring the volume of carbon dioxide produced ... 

Buffer Reaction Mechanism. The mechanism by which adipic acid buffers the pH is simple. It reacts with lime or limestone in the effluent hold tank to form calcium adipate. In the absorber, calcium adipate reacts with absorbed S02(H2S03) to form CaS03 and simultaneously regenerates adipic acid (the buffer reaction). The regenerated adipic acid is returned to the effluent hold tank for further reaction with lime or limestone. With a sufficiently high concentration of calcium adipate in solution, usually on the order of 10 m-moles/liter to react with the absorbed S02, the overall reaction rate is no longer controlled by the dissolution rate of limestone or calcium sulfite. 

EXPLOSION and FIRE CONCERNS moderate fire hazard in form of dust and powder, when exposed to flame or by spontaneous chemical reaction NFPA rating Health 4, Flammability 1, Reactivity 1 slight explosion hazard in the form of powder or dust mixtures of the powder with carbon tetrachloride or trichloroethylene will flash or spark on impact reacts incandescently with fluorine or chlorine decomposition emits very toxic fumes of Beryllium oxide incompatible with acids, caustics, strong oxidizers, chlorinated hydrocarbons, and molten lithium use dry sand, dry clay, dry ground limestone, or other methods for firefighting purposes. 

Acidizing with HF finds no application in carbonates, as it forms solid calcium fluoride (CaF ) in limestone and both calcium fluoride and magnesium fluoride (MgF ) in dolomite. In any case, HF reaction in sandstones cannot be considered analogous to HCl reaction in carbonates. Whereas HF reaction in sandstones is controlled by the surface area of siliceous minerals—that is, by the surface reaction kinetics—HCl reaction in carbonates is controlled by the mass transport of acid to the mineral surfaces. In sandstones, the acid transport rate is high compared to surface reaction rates, and in carbonates, surface reaction rates are high compared to the acid transport rate. The slower rate step (acid transport or surface reaction) will control the reaction kinetics. Overall, HCl reactions in carbonates are much fester than HF reactions in sandstones. 

Formation con osition. The chemical and physical compositions of the formation are very important in defining the acid spending time, and, subsequently, the acid penetration distance. Acid spends very rapidly in highly reactive (>95%) carbonates. Acid spending time can be much slower in formations with lower HCl reactivity (65%-85%). As mentioned previously, the reaction rate of acid in limestone is about twice that in dolomites (at lower temperatures). Therefore, live acid penetration can be deep in low-solubility, lower-temperature dolomites. 

The buffering activity of adipic acid limits the drop in pH that normally occurs at the gas-liquid interface during SO2 absorption, and the resultant higher concentration of SO2 at the interface significantly accelerates the liquid-phase mass transfer. The capacity of the bulk liquor for reaction with SO2 is also increased by the presence of calcium adipate in solution. Thus, the SO2 absorption becomes less dependent on the dissolution rate of limestone or calcium sulfite in the absorber to provide the necessary alkalinity. 

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