pH yog qhov tseem ceeb tshaj plaws uas cuam tshuam rau kev ua haujlwm ntawm txhuas ntsev coagulants. Nws ncaj qha txiav txim siab daim ntawv, cov khoom hluav taws xob, thiab coagulation mechanism ntawm txhuas ntsev hauv dej, thaum kawg cuam tshuam cov coagulation nyhuv.
Thaum txhuas ntsev (xws li txhuas sulfate Al₂(SO₄)₃ thiab txhuas chloride AlCl₃) ntxiv rau hauv dej, lawv raug hydrolysis sai, tsim ib tug series ntawm mononuclear thiab polynuclear hydroxyl complexes, nws thiaj li tsim amorphous aluminium hydroxide Al (OH) ₃ precipitate. Hom thiab kev faib ua feem ntawm cov khoom siv hydrolysis no yog nyob ntawm pH.
Al³⁺ + H₂O ⇌ Al(OH)²⁺ + H⁺
Al³⁺ + 3H₂O ⇌ Al(OH)₃ (amorphous) + 3H⁺
Raws li pH nce, cov khoom siv hydrolysis yog raws li hauv qab no: Al³⁺ → Al(OH)²⁺, Al(OH)₂⁺ → Al(OH)₃(s) → Al(OH)₄⁻ (aluminate, soluble).
Haus dej -qib polyaluminum chloride (khoom), tshuaj tsuag- siv polyaluminum chloride (PAC), polyaluminum chloride, polymeric coagulant
1. Nyob rau hauv qhov qis pH ntau (feem ntau<5.5)
Feem ntau yog tsim los ntawm cov khoom muaj txiaj ntsig zoo mononuclear complex ions (xws li Al³⁺, Al (OH)²⁺). Cov ions muaj txiaj ntsig zoo no ua rau muaj txiaj ntsig zoo ntawm cov txheej txheem colloidal ob txheej, ua rau tsis zoo rau cov khoom siv colloidal (xws li impurities nyob rau hauv feem ntau cov dej ntuj), ua rau destabilization.
Cov nyhuv tshem tawm turbidity feem ntau yog nruab nrab, tab sis nws muaj txiaj ntsig zoo hauv kev tshem tawm cov teeb meem tsis zoo hauv cov organic (xws li qee cov humic acids). Cov tsim flocs yog me me thiab xoob.
Hauv cheeb tsam no, qhov ua tau zoo ntawm txhuas ntsev yog qhov cuam tshuam ntau dua hauv kev them nqi nruab nrab, tab sis cov seem ntawm cov txhuas seem yuav siab vim tias tsis txaus Al (OH)₃ nag lossis daus tsis tuaj yeem tsim. Thaum pH <4, txhuas muaj nyob rau hauv daim ntawv ntawm Al³⁺, uas ua rau tsis zoo coagulation.
2. Qhov zoo tshaj pH ntau yam (feem ntau 6.0-7.8)
Feem ntau, hluav taws xob nruab nrab amorphous aluminium hydroxide Al(OH)₃(s) precipitates, thaum tib lub sij hawm tsim ib tug ntau ntawm polynuclear hydroxyl complexes nrog network lug (xws li Al₁₃O₄(OH)₂₄⁷⁂s), piv txwv li, Al₁₃O₄ (OH) ₂₄⁷⁺ .
Thaum lub sij hawm nws tsim, Al(OH)₃ ua zoo li lub vas loj, ncaj qha encapsulating thiab cheb cov colloids thiab tshem tawm cov khib nyiab hauv dej rau co- nag lossis daus. Nyob rau tib lub sijhawm, polynuclear polymers txuas qhov sib txawv ntawm cov khoom tsis ruaj khov, tsim loj, ntom flocs. Qhov no yog thaj av uas muaj txiaj ntsig zoo tshaj plaws hauv kev tshem tawm turbidity, xim, thiab ntau yam pa phem.
3. High pH Zone (typically >8.5)
Al(OH)₃ precipitates redissolve, tsim tsis zoo nqi soluble complex ions Al(OH)₄⁻. Hauv qhov no, kev them nyiaj nruab nrab tsis ua haujlwm, thiab cov nyhuv cheb ploj mus. Coagulation efficiency deteriorates sharply, thiab cov tsim flocs redissolve (restabilize), ua rau cov dej ua turbid dua.
Thaum pH> 8.5, lub solubility ntawm txhuas nce ntxiv. Ntawm pH> 9, txhuas muaj nyob rau hauv daim ntawv ntawm Al (OH) ₄⁻, coagulation tsis ua hauj lwm, thiab cov residual txhuas concentration nce ntxiv, muaj peev xwm tshaj 0.2 mg / L.
Thaum siv cov ntsev txhuas rau coagulation, lub cev pH (tshwj xeeb tshaj yog cov pH tam sim ntawd tom qab sib tov) yuav tsum tau hloov kho kom pom qhov zoo. Rau txhuas sulfate, lub hom phiaj pH feem ntau yog nyob ib ncig ntawm 7.0. Lub hydrolysis ntawm txhuas ntsev siv alkalinity (HCO₃⁻) hauv dej, tso H⁺ thiab ua rau txo qis pH. Yog tias cov dej nyoos alkalinity tsis txaus (<50 mg/L as CaCO₃), lime (CaO) or sodium carbonate (Na₂CO₃) must be added to maintain pH stability.