Phosphates Flashcards
What group does phosphorus belong to in the periodic table, and what is its oxidation state?
Phosphorus belongs to Group VA and has an oxidation state of +5.
Name the three allotropes of phosphorus and describe their properties.
- White phosphorus: Simplest elemental form (P4 tetrahedron), waxy solid, highly reactive due to a small P–P–P angle (60°).
- Red phosphorus: Structure unknown, used in explosives, fireworks, and matchboxes.
- Black phosphorus: Formed by heating white phosphorus under high pressure; has a layered structure similar to graphite.
What are the oxoacids of phosphorus, and how do they differ in their properties?
- Phosphoric acid (H3PO4): Triprotic (3 H+ ions). Produces salts with PO4³⁻.
- Phosphorous acid (H3PO3): Diprotic (2 H+ ions), with one hydrogen covalently bonded to phosphorus. Produces salts with HPO4²⁻.
What are the main mineral sources of phosphorus?
- Apatite: Complex calcium phosphate (Ca5(PO4)3(F,Cl,OH)).
- Fluorapatite (Ca5(PO4)3F): Found in granitic and metamorphic rocks.
- Hydroxyapatite (Ca5(PO4)3OH): Main component of animal bones and teeth.
What are phosphorites, and how are they processed?
Phosphorites are marine sediment-derived phosphates mixed with limestone, quartz sand, and clay. They are processed in beneficiation plants to separate valuable components.
What are the two primary methods for converting phosphate rock into useful products?
- Furnace/Thermal Process: Produces elemental phosphorus via high-temperature reactions with silica and carbon.
- Wet Process: Reacts phosphate rock with sulfuric acid to produce dilute phosphoric acid, later concentrated for use in fertilizers.
What is the main impurity issue in the Wet Process, and how is it handled?
Fluorine and other impurities (Fe, Mg, Al) are carried over into phosphoric acid. Large volumes of phosphoric acid and sulfuric acid are used to maintain reactions and reduce coating of phosphate rock by calcium sulfate.
What are sodium phosphates, and how are they classified?
Sodium phosphates are salts of phosphoric acid made by neutralizing it with sodium carbonate or sodium hydroxide. They are classified into orthophosphates, crystalline condensed phosphates, and glassy condensed phosphates.
What is the principal use of sodium tripolyphosphate?
It is used as a builder in detergents to enhance cleaning efficiency.
What are ordinary superphosphates (OSP), and how are they made?
OSPs are the oldest manufactured phosphate fertilizers, containing 16–20% P2O5. They are made by reacting phosphate rock with sulfuric acid.
How is triple superphosphate (TSP) different from OSP?
TSP is made by acidulating phosphate rock with phosphoric acid, resulting in a higher P2O5 content (45–46%).
Name other types of phosphate fertilizers and their uses
- Ammonium phosphates (e.g., DAP, MAP): Used in NPK formulations.
- Nitric phosphates: Require less sulfur and reduce shipping costs.
- Potassium phosphates: Produced by reacting phosphoric acid with potassium chloride.
What by-products are generated from the Wet Process, and how are they used?
- Phosphogypsum: Used for soil improvement, plaster, and cement.
- Fluorine recovery: As hydrofluoric acid or fluosilicic acid.
- Uranium recovery: Extracted from phosphate rocks with trace uranium content.
- Animal feed supplements: Calcium phosphates (dicalcium and monocalcium phosphate)
What are the major environmental concerns in phosphate production?
- Dust and noise control during mining.
- Handling of slimes and tailings ponds.
- Restoration of mined-out areas.
- Control of fluorine emissions and other particulates.
What are the industrial applications of phosphoric acid?
- Food industry (e.g., soft drinks, candy).
- Fertilizers (e.g., superphosphates).
- Manufacturing detergents, fire retardants, and plasticizers.
- Metal treatment methods
How are nitrophosphates advantageous over other phosphate fertilizers?
They require less or no sulfur, reducing shipping costs for sulfur.
What are the main environmental issues in phosphate mining and processing?
- Dust and noise pollution during mining.
- Management of slimes and tailings ponds.
- Control of fluorine and other emissions.
- Restoration of mined-out areas.
