碳酸盐的基本介绍

碳酸鹽的基本介紹碳酸鹽礦物分類基本物理性質基本化學性質化學平衡反應與自由能溶度積和溶解度方解石族：六方晶系―R3C方解石(Calcite)：CaCO3菱鎂礦(Magnesite)：MgCO3菱鐵礦(Soderite)：FeCO3菱錳礦(Rhodochrosite)：MnCO3菱鋅礦(Smithsonite)：ZnCO3

特性為最重要的碳酸鹽礦物，有完全的菱面體解理，玻璃光澤，透亮至半透亮，一般為白色或無色，含有其他顏色亦不少，條痕白色，硬度3.0，比重2.71，可溶於稀鹽酸而起泡，純淨透亮的稱為冰洲石(IcelandSpar)，具有強烈雙折射和完全解理。方解石Calcite分布与产状石灰岩、大理岩和美麗的鐘乳石之主要礦物即為方解石。在泉水中可沉積出石灰華，在火成岩內亦常為次生礦物，在玄武岩流的杏仁孔穴中，沉積岩之裂縫內常有方解石充填而成細脈，或透過生物學作用，以貝殼或岩礁的方式產出。霰石族：斜方晶系―Pmcn霰石(Aragonite)：CaCO3毒重石(Witherite)：BaCO3菱鍶石(Strontianite)：SrCO3白鉛礦(Cerussite)：PbCO3

特性文石由霰石、方解石、鐵氧化物、蛋白石等礦物所組成屬次生礦物，其中以霰石為主要成分，呈葡萄狀或球狀集合體，硬度為3~4，比重3.0，良質文石顏色較深，硬度高，花紋多變化，具有同心圓構造。黃色、乳白色、無花紋屬中級文石。文石Aragonite

(霰石)分布与产状文石賦存於多孔質玄武岩的氣孔和裂隙內，生成過程似在氣孔的圍岩壁上先生成一層綠泥石或褐鐵礦薄膜，文石眼生於其上，最後再填充霰石或方解石於其空隙中。礦石構造有：塊狀構造，各種礦物成不規則混合。縞狀構造，以霰石及玉髓等數種不同礦物，形成明顯之同心縞狀充填其中。白雲石族：六方晶系―R3白雲石(Dolomite)：CaMg(CO3)2鐵白雲石(Ankerite)：CaFe(CO3)2

特性由碳酸鈣和碳酸鎂構成的礦物，CaCO3和MgCO3的比例，大致是1:1，菱面結晶，有完整的解理，硬度3.5，比重2.9，顏色多為白色至肉紅色，有玻璃光澤，在冷稀酸中不起泡，粉末則緩慢起泡。分布与产状存在於結晶石灰岩以及其他富含鎂的變質岩中，部分產於熱液礦脈和碳酸鹽岩石的孔穴內，偶爾作為各種沉積岩的膠結物，為碳酸鹽岩石中為最常見的一種造岩礦物。台灣白雲石之造成係鎂質交換石灰岩之鈣質而成，主要賦存於先第三紀大南澳片岩下部之結晶石灰岩帶，呈凸鏡體、層狀或不規則礦囊。具(OH)之單斜晶系碳酸鹽孔雀石(Malachite)：Cu2CO3(OH)2藍銅礦(Azurite)：Cu3(CO3)2(OH)2

LAWOFMASSACTIONConsiderthereaction:aA+bBcC+dDWherea,b,canddarethemolaramountsofcompoundsA,B,CandD,respectively.Atequilibriumitmustbetruethat:K(theequilibriumconstant)isindependentofconcentration.Thus,ifwe,forexample,increaseaA,thentomaintainequilibrium,thereactionmustshifttotherightsothattheactivitiesofthereactantsdecreaseandtheactivitiesoftheproductsincrease,keepingKconstant.ThisisanexampleofLeChatlier’sPrinciple.LawofMassActionLeChatlier’sPrinciplebasedonthelawofmassaction.Itstatesthat:ifareactionisperturbed,thenthatreactionwillproceedinadirectionsoastolessentheeffectoftheperturbation.Forexample,ifthereactionisinitiallyinequilibrium,andweincreasetheconcentrationofreactantA,thenthereactionmustproceedtotherighttodecreasetheactivitiesofAandB,andincreasetheactivitiesofCandD,andtherebykeeptheratioofproductandreactantactivitiesconstant.GibbsFreeEnergy,GAmeasureofareaction’sabilitytoaccomplish“useful”work,thatis,energyreleasedbythereactionthatcanbeconvertedtowork.-Aportionofthenenergyinvolvedinachemicalreactionisunavailabletodowork.ReallyinterestedinthechangeintheGibbsfreeenergy,ΔG°,ofareaction:ΔGr°=ΔHr°-TΔSr°T=temperaturein°K(°C+273.15°)ΔHr°=thechangeinenthalpy,ortheheattransferbetweenasystemanditssurroundingsforaprocessunderconstantpressure.Considertheformationofliquidwaterfromgaseousoxygenandhydrogen:H2(g)+½O2(g)=H2O(l)25.5L12.3L0.018L00 -68.315kcal/mol ΔH°=-68.315kcal/mol highlyexothermicΔSr°=changeinentropy

(degreeofrandomnessordisorderinthesystem) (e.g.liquidH2OVaporH2OhasapositiveΔS)

S°(ice)<S°(water)<S°(vapor) 10.68<16.72<45.11cal/molKHOWDOWECALCULATEK?Fortheabovereaction,wecanwrite:rG°=cfG°C+dfG°D-afG°A-bfG°BAndwealsowrite:whereRisthegasconstantandequals8.314JK-1mol-1or1.987calK-1mol-1.DeterminetheKspofcalciteat25°CCaCO3

Ca2++CO32-TheactivityofsolidCaCO3=1Fromtables:Species ΔGf°(kJ/mol) Ca2+ -553.6 CO32- -527.0 CaCO3 -1128.4ΔGr°=ΔGf-products-ΔG°

f-reactantsΔGr°=(-553.6)+(-527.0)–(-1128.4)=+47.8kJ/molUsinglogK=-ΔGr°/2.3026RTlogKsp=-8.37andK=10-8.37Calculatethesolubilityproductofdolomiteat25°C:CaMg(CO3)2(s)Mg2++Ca2++2CO32-rG°=fG°Mg2++fG°Ca2++2fG°CO32--fG°CaMg(CO3)2(s)rG°=-455.5+(-553.6)+2(-527.0)-(-2161.3)=98.2kJmol-1SolubilityProductsTHEIONACTIVITYPRODUCT(IAP)Consideronceagainthereaction:CaSO4(s)Ca2++SO42-Theequilibriumconstantisexpressedintermsoftheactivitiesofthereactantsandproductsatequilibrium:However,arealsolutionmayormaynotbeinequilibrium.Theionactivityproduct(IAP)orreactionquotient(Q)hasthesameformastheequilibriumconstant,butinvolvestheactualactivities:THESATURATIONINDEXThesaturationindex(SI)isdefinedaccordingto:IfIAP=KSP,thenSI=0,andthewaterissaturatedwithrespecttothemineral.IfIAP<KSP,thenSI<0,andthewaterisundersaturatedwithrespecttothemineral.IfIAP>KSP,thenSI>0,andthewaterissupersaturatedwithrespecttothemineral.AnAPPLICATIONAwatercontainsthefollowing:3.13x10-4molL-1Mg2+;8.48x10-4molL-1Ca2+;and2x10-6molL-1CO32-.Determinewhetherthiswaterissaturatedwithrespecttodolomite(CaMg(CO3)