Producto de Solubilidad MmAn(s)  mMn+ + nAm- Ejemplo: precipitación del ion férrico Fe(OH)3(s)   Fe3+ + 3OH- Ksp(hidróxido) = [Fe3+][OH-]3 = 10-38.8 FeO(OH)(s)  + H2O  Fe3+ + 3OH- Ksp(goetita) = [Fe3+][OH-]3 = 10-41.5 ½Fe2O3(s)  + 1½ H2O  Fe3+ + 3OH- Ksp(óxido) = [Fe3+][OH-]3 = 10-42.7

Equilibrios reportados (NIST) Fe3+ + OH-  FeOH2+ Fe3+ + 2OH-  Fe(OH)2+ Fe3+ + 3OH-  Fe(OH)3 Fe3+ + 4OH-  Fe(OH)4- 2Fe3+ + 2OH-  Fe2(OH)24+ 3Fe3+ + 4OH-  Fe3(OH)45+

At 25°C, K1 = 6.46x1011 K2 = 2.51x1022 K3 = 2.51x1030 K4 = 2.51x1034 K22 = 1.26x1025 K34 = 5.01x1049 Ksp = 2.51x10-39

Solubilidad total del ion férrico

Distribución de Especies Solubles

Adición de un Agente Complejante EDTA Fes = [Fe3+] + mi[Fem(OH)n] + Fe(EDTA)p+ = [Fe3+] + Kmn[Fe]m[OH]n + KFeEDTA[Fe][EDTA] EDTATotal = [EDTA] + [Fe(EDTA)p+] = [EDTA] + KFeEDTA[Fe][EDTA] Despejando [EDTA],

Agregación de un Agente Complejante Adicional

Distribución de Especies Solubles (c/EDTA)

Representación Gráfica de la Distribución 3Fe3+ + 4OH-  Fe3(OH)45+ K34

pH Natural de una Solución Fe3+ + OH-  FeOH2+ K1 Fe3+ + 2OH-  Fe(OH)2+ K2 Fe3+ + 3OH-  Fe(OH)3 K3 Fe3+ + 4OH-  Fe(OH)4- K4 2Fe3+ + 2OH-  Fe2(OH)24+ K22 3Fe3+ + 4OH-  Fe3(OH)45+ K34 H2O  H+ + OH- Kw Fe total soluble (Fes) = [Fe3+] +  m[Fem(OH)n]i OH total = OHTotal = [OH-] +  n[Fem(OH)n]i Disociación del agua   = moles de agua disociada Kw = [H+][OH-] = ([H+]o + )([OH-]) OHTotal = [OH-]o +  3 incógnitas ([Fe3+], [OH-] & ), 3 ecuaciones pH natural depende de Fes, anion & T

Economía de la Precipitación & Disolución Pagamos por todo lo que agregamos. Costos de reactivos Costos de remediación Veremos de cerca el proceso de precipitación con hidróxido $  por cada Fe3+, 3 OH- (Fe(OH)3 + complejos solubles $  Desechos sólidos $  Contaminación de la solución con cationes (Na+, Ca2+ or Al3+)

Caso interesante – Cobre c/glicina NH2CH2COOH – Glicina (Gly) - HL NH2CH2COO- + H+  NH2CH2COOH NH2CH2COO- + 2H+  NH3CH2COOH+ Cu2+ + NH2CH2COO-  NH2CH2COOCu+ Cu2+ + 2NH2CH2COO-  (NH2CH2COO)2Cu

Sistema Cu-Glicina – f(pH) Cu(II) especies: Cu2+, Cu(Gly)+ and Cu(Gly)2 ¿Cuales otras especies debería considerarse? Especies insolubles (las que queremos): CuO & Cu(OH)2 Especies solubles: CuOH, Cu2(OH)3+, Cu2(OH)22+ & Cu3(OH)42+ El sistema global depende del pH

Pirometalurgia de calcopirita

Fundición (smelting) Concentrates (CuFeS2) Flux (SiO2) Coal (C,H)   Concentrates (CuFeS2) Flux (SiO2) Coal (C,H) Oxygen (O2) Air (N2,O2) 25 °C Natural Gas (C,H) Isasmelt Furnace Isasmelt Lance Off Gases 1300°K (CO2,SO2,H2O,N2) 10CuFeS2 + 15½O2 + 3½SiO2  5Cu2S + 3FeS (matte) + 3½Fe2SiO4 (slag) + 12SO2 (gas) 1300°K Rotary Holding Furnace Diagram courtesy of Xstrata Copper CuFeS2 + 1.55O2 + 0.35SiO2  0.5Cu2S + 0.3FeS (matte) + 0.35Fe2SiO4 (slag) + 1.2SO2 (gas) 1300°K Image Description: 1. The furnace is where the first of the reactions takes place. The bricks are chrome magnesium bricks and the roof is made of water cooled copper blocks. 2. The lance allows these gases to be introduced into the mixture 3. These are the products that are fed into the reaction – the Concentrates from the stacker/reclaimer, additional silica called flux and coal as a carbon source. 4. The additional O2 is added so that the reaction can take place. Natural Gas is taking the place of coal as the carbon source. 5. These are the gaseous products of the reaction. SO2 is the product with the potential to do the most damage as it converts to sulphuric acid in the atmosphere. These days these gases are trapped and used to make fertiliser. 6. This is the overall reaction for this stage. Iron/Silica material is called slag and is a waste material. Matte is the form the copper is now in. In reality the slag still contains copper and is reused to control the temperature of the reaction. Other copper containing waste from around the site is also fed back into the process.

Tabla de moles (una para cada fase) Componentes sólidos Moles alimentados Moles producidos CuFeS2 nCuFeS2 - SiO2 0.3nCuFeS2 Cu2S 0.5nCuFeS2 FeS CuFeS2 + 1.55O2 + 0.3SiO2  0.5Cu2S + 0.3FeS + 0.35Fe2SiO4 (slag) + 1.2SO2 (gas) 1300°K Componentes líquidos Moles alimentados Moles producidos Fe2SiO4 - 0.35nCuFeS2 Componentes gaseosos Moles alimentados Moles producidos CH4 nCH4 - O2 1.55nCuFeS2 + 2nCH4 N2 3.79nO2 CO2 H2O 2nCH4 SO2 1.2nCuFeS2 CH4 + 2O2  CO2 + 2H2O 1300°K

Energy Balance For systems with reactions, T0 = 298°K & HTo = ΔHf     For systems with reactions, T0 = 298°K & HTo = ΔHf If there is a phase change (pc), then   T0 Tpc T  

DATA 298°K Chalcopyrite (CuFeS2) Quartz (SiO2) Natural gas (CH4)       Oxygen (O2) Nitrogen (N2)     1300°K Chalcocite (Cu2S) Nitrogen (N2) Water (H2O)       Troilite (FeS) Sulfur Dioxide (SO2) Carbon Dioxide (CO2)       Fayalite (Fe2SiO4)  

Conversión Pierce Smith Converter 1500°K Flux (SiO2) Off Gases (SO2) Matte (Cu2S FeS) Air (N2,O2) Oxygen (O2) Flux (SiO2) Slag Copper Blow Cu2S + O2  2Cu (blister) + SO2 (gas) Blister Copper Slag Blow 2FeS + 3O2 + SiO2  Fe2SiO4 (slag) + 2SO2 (gas) Off Gases (SO2) Pierce Smith Converter Diagram courtesy of Xstrata Copper Image Description: Teaching Tip: Background: Molten copper matte is transferred by cast steel ladles to the converters where silica is added causing an iron slag to form. Sulphur is removed as an off gas and the slag is also removed from the matte.