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This 4 page Class Notes was uploaded by Sabina Okuneva on Saturday September 12, 2015. The Class Notes belongs to GEOL 3020 at University of Georgia taught by Staff in Fall. Since its upload, it has received 56 views. For similar materials see /class/202260/geol-3020-university-of-georgia in Geology at University of Georgia.
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Date Created: 09/12/15
Chemical weathering reactions The mineral assemblage formed during the weathering process depends upon three factors 0 The mineralogical and textural composition of the parent rock 0 The composition and temperature of the aqueous solutions 0 The uid flow ie rate of water flow and pore network Water composition and ow rate ie Rates of reaction The formation of minerals in the weathering environment is primarily the result of reaction between protons ie H in ground waters and primary silicate minerals Also important are reactions involving electron transfer ie redox reactions Although the primary source of protons is a result of the production of organic acids in soil not the absorption of atmospheric COZ by rain water the production of acids can be viewed as the production of carbonic acid This is because organic acids in surface soils readily oxidize to carbon dioxide The oxidation of oxalic acid is shown below 4 HOZCQOZH 202 77gt 8COZ 4HZO Recalling that carbonic acid forms by the reaction HZO COZWgt HZCO3 At most soil pH conditions the carbonic acid immediately dissociates to bicarbonate and protons HZC03 77gt HCOg39 H Example 1 A typical weathering reaction in dilute waters with high acidity can be represented by reaction with ablite 7 H20 H NaAlSi3O8 mgt AlOH3 Na 3 H5104o The stability fields for gibbsite kaolinite idealized smectite Naibeidellite and endimember albite are considered in the diagram below Unlike our previous example where we fixed the concentration of dissolved silica by quartz saturation in this example the amount of dissolved H Na H48i04O and are allowed to vary Recalling that Gibb s phase rule requires us to limit the degrees of freedom in our system temperature and pressure must remain constant for the construction of a stability diagram that allow us to vary dissolved species Recall also that the activity of solids and water are unity The diagram below depicts concentrations in brackets which indicates moles per liter By doing so this allows us to use the stoichiometry of the reactions to determine how much the solution composition changes as reactions proceed Also in this example we will consider the situation where there is an excess of albite in the system 11 m 9 8 7 a 36 E g5 A 3 z Albme Opalme 5111 5 meme Kauunme 75 VA 73 z 71 lug rHAsmA m mu m mmymd msdn z w W m 53mm mpsm WW m m w mamvd swasymued m mm mm mm m Imeme 5ame w w m mm m mmwmmm wwmmwanmsymm mmm mm ma H mm 51m m mmmmm mm mm mm a mm mz zmzusxofmyr mum meulpzumme a x m 612ka zhme 1 my th5 m w m u mam minku ha z m a mm mm mmmmmd a 5th m mss sxofcmhma m w s sunbexvgymd wed m w mu Mvgcmssmed w m m mm m m m mm y H10 m mum gtmiso40momz39oo a mm mm mwm m zAlAOHAozusxo 51m 0 As Embasdhydmu WWW mmmmmmnm mm 153mm my th gt shown smo ma xaacm mm mm zmxususedm we 112mm um man no mmm mwmny was a quotmm and um mm um m a 5 0m an mm Emma m nmmymm m mm Dnuds m Exam 6 m a mm mm mm m no m m m m n mm mm m mm mmmnm m m mm mm mmxywumm mm s w a Aeolian zzmmm gtNw ln jp 40mnl mu Mme mzsmoozzn39ozzmmsgox gtAxsa040 x zzmwuusxw gt NLJ h kO XOHL 2 we 115M994 n mmzmu mo 7 my a ram mymmm mm m m e mm mm mmmm s mwmdzmeqmmmm wage a mxmmmm New Nu 115M994 m zwonzmw 16HampO lt gtNz wnap 40m ozvs p Dump 2 my Wm mum wavegmmxs yudwsy m ml ems m m mm m hydmdyvnmw aw a mmquot a cmmzl a mam mm mm vusz suns anewdm qurunhsphy h EMMMW MM paung z plxsmmagk m dualquot helmShams m ammummwwm yummy Fwy mug mamas mmmmjman may wmamm Enumka mmsm GA mth mama39an c hummeme zu un aqua Tznlzmmngnm Iz mmm my kw