Comprehensive Notes: Analysis for Salts

Salts from Minerals

• Salts are naturally present in water and soil; they originate from minerals dissolved during the water cycle. Water runs through soil and rocks, dissolving solid mineral deposits and transporting salts into lakes, rivers, creeks, etc. The center of Australia (Lake Eyre) was once underwater; the extreme salinity seen there is a historical example of how salts accumulate in water bodies.

• Lake Eyre (dry most years) shows very high salt concentrations when contains water; salts deposit on the bed when it dries.

• Common reference: Sodium chloride, NaCl, is often called “salt”; in soil/water contexts, “salt” refers to any ionic compound present in water/soil.

• Sources of salts in water/soil include minerals, heavy metals, and organometallic substances. A key topic is how salt concentrations are measured.

Salts from Minerals

• Water cycle role: Dissolves mineral deposits as it travels through rocks and soil; transports salts to lakes, rivers, and other water bodies.

• Geological history example: The centre of Australia was underwater; Lake Eyre salt presence is consistent with ancient marine influence.

• Victoria regional examples with high mineral concentrations:

  • Hepburn Springs: Renowned for mineral springs; ions include Na^+, K^+, Ca^{2+}, Mg^{2+}, Fe^{2+}, Cl^-, HCO_3^-, etc.

  • Wimmera Mineral Sands: Sandy soils rich in zirconium and titanium minerals; Iluka Mines operates in the region to extract these minerals.

  • Pittong clay mine: High clay mineral content near Pittong (Central Victoria); clay is a mix of pittongite (tungsten-bearing) and kaolin (a white clay used in cosmetics/pottery).

• Area of Study 2 context: How chemicals are measured and analysed; focus on salts from minerals as one source category.

Salts from Human Activity

• Human activities raise salt levels in water/soil; often viewed as pollution.

• Regulation: Many countries monitor/regulate dissolved salts and contaminants in waterways.

• Major contributing sectors:

  • Mining: Large water use in ore processing; discharge of ion-containing water; dust from sites can contaminate soil.

  • Agriculture: Fertilisers (dissolved by rain/runoff) increase nutrient/salt load in waterways; common Australian fertilisers include NH4NO3, (NH4)2SO4, and Ca(H2PO4)2.

  • Excess nutrients can cause eutrophication: algal blooms reduce dissolved oxygen, harming aquatic life; nodular blue-green algae can produce toxins.

  • Domestic sources: Historically, phosphate-based detergents added phosphates to water; phosphates promote algal blooms; eutrophication consequences include fish kills and toxic algal blooms.

  • Sewage treatment plants: Treat effluent and grey water; effluent can still contain various ions similar to domestic sources.

  • Stormwater: Rain washes off surfaces (carparks, roofs, roads); transport soils, dust, debris, petrochemicals into waterways.

  • Industry: Industrial wastes can contain salts; legacy contamination at sites dating to late 1800s/early 1900s in Victoria.

• Heavy metal salts: A subset of salts from human activity that are particularly toxic; see Heavy Metals section for details.

Heavy Metal Salts

• Definition: Heavy metals typically refer to metals with high density that can be toxic; common examples include Cu, Pb, Cd, Cr, Ni, Zn, As, Hg; some classify Al and others as toxic depending on context; metalloids like arsenic are sometimes included due to toxicity.

• Densities: Heavy metals are contrasted with lighter, non-toxic elements like Al and Mg; density data illustrate relative heaviness (Figure 16.1.4 reference).

• Table 16.1.1 (summary): sources and human health effects of several heavy metals

  • Copper (Cu): Essential for metabolism; used in copper pipes; required for red blood cell production; essential in small amounts.

  • Lead (Pb): From lead pipes, batteries, paints, ammunition, cosmetics; non-essential; toxicity includes anemia and nervous system effects; historically widespread in paints and petrol.

  • Cadmium (Cd): From smelting, batteries, paints, fossil fuel combustion; non-essential; toxicity includes kidney damage and bone effects.

  • Nickel (Ni): From power plants, waste incinerators, batteries disposal; non-essential; health concerns.

  • Zinc (Zn): From mining, smelting, steel production; essential in trace amounts; deficiency/toxicity depending on dose; deficiency affects enzymatic functions; high exposure causes gastrointestinal issues.

  • Arsenic (As): Natural deposits and industrial sources; non-essential; carcinogenic and systemic toxicity.

  • Mercury (Hg): From agricultural processes, burning fuels, industrial processes; non-essential; neurotoxicity with brain/nerve damage.

• Persistence and bioaccumulation:

  • Once released, heavy metals persist in environments and accumulate in soils/water and organisms.

  • Bioaccumulation: concentrations increase up the food chain, leading to higher exposure in top predators (bioaccumulation illustration in Figure 16.1.5).

• Organometallic compounds:

  • Definition: Compounds with at least one direct bond between a metal atom/ion and a carbon atom; can be highly polar if the metal has low electronegativity.

  • Common industry use: Catalysts or reagents in chemical processes.

  • Example: Tetraethyl lead, $Pb(C2H5)_4$, used in petrol historically to improve combustion; now banned due to health risks from atmospheric deposition.

  • Formation of organometallic salts: e.g., methylmercury salts like $CH3HgCl$, $CH3HgOH$ form when mercury compounds are processed or combusted; toxicity is heightened because methylmercury is readily transported in the body.

• Organometallic toxicity: Heavy metal ions are toxic when present as water-soluble cations or as organometallic compounds.

Case Study: Lasting impact of heavy metals

• Mercury poisoning in Minamata, Japan (1950s): Factory discharged methylmercury into bay; local seafood-based diet led to accumulation in humans.

• Early indicators: Cats in the town exhibited bizarre dancing behavior before collapse due to mercury poisoning; neurological symptoms in people followed.

• Long-term consequences: Irreversible brain/organ damage, congenital disorders in children born to affected parents; Minamata disease identified as mercury-related.

Organometallic Compounds: Industry and Transport

• Example: Methylmercury – very toxic and mobile within organisms; forms in some industrial processes (e.g., ethyne production) and during combustion of mercury-containing compounds.

• Tetraethyl lead ($Pb(C2H5)_4$) as an industrial organometallic catalyst/additive in fuels; led to environmental deposition on soils and waterways; health risks prompted ban.

Organic and Inorganic Salts in Water Systems

• Heavy metals and organometallics contribute to the salinity/contaminant load of water and soils; monitoring helps protect drinking water and ecosystems.

• The overall message: Many salts are essential in trace, beneficial roles, but excessive or inappropriate forms/amounts are harmful.

Hard Water and Its Effects

• Hard water definition: Water that requires a lot of soap to obtain lather; caused by dissolved metal ions (mainly $Ca^{2+}$, $Mg^{2+}$, $Mn^{2+}$, $Fe^{2+}$).

• Mechanism with soap: Soap provides stearate ions ($C{17}H{35}COO^-$). Multivalent metal ions bind these ions to form insoluble precipitates, reducing lather and forming deposits on pipes (limescale).

• Precipitation reaction (example):
  2C{17}H{35}COO^-(aq) + Ca^{2+}(aq)
  ightarrow Ca(C{17}H{35}COO)_2(s)

• Consequences: Deposit buildup inside pipes; potential pipe blockage from crystalline deposits (limescale Figure 16.1.8).

Testing for Salinity: Electrical Conductivity (EC)

• Principle: Pure water is a poor conductor; adding soluble salts increases ion concentration and conductivity.

• Simple test: A light bulb in a circuit with two electrodes in a water sample will show brightness proportional to conductivity (Figure 16.1.9).

• Quantitative measurement: Include a meter in the circuit to quantify conductivity.

• Conductivity-concentration relationship: At low salt concentrations, conductivity increases linearly with ion concentration (Figure 16.1.11/16.1.10 context).

• Unit: Electrical conductivity measured in micro-Siemens per centimeter, $\mu S\,cm^{-1}$.

• Temperature effect: Conductivity increases with temperature; measurements are standardized at $25^{\circ}$C for consistency; temperature-compensated meters adjust readings for other temperatures.

• Electrode geometry: Distance between electrodes is fixed/independent to allow comparisons across devices.

EC Guidelines for Water Use (Table 16.1.4)

• EC ranges and uses (approximate):

  • $0$ to $800$ $\mu S\,cm^{-1}$: Good drinking water; suitable for irrigation and livestock.

  • $800$ to $2500$ $\mu S\,cm^{-1}$: Unpleasant to drink; irrigation use requires management.

  • $2500$ to $10000$ $\mu S\,cm^{-1}$: Not recommended for human consumption; suitable for salt-tolerant vegetation only.

  • $>10000$ $\mu S\,cm^{-1}$: Not suitable for any plants or animals.

  • Ocean water baseline: Around $40000$ to $56000$ $\mu S\,cm^{-1}$ (typical ocean range).

• Practical use: Helps determine appropriate uses of water (drinking, irrigation, ecosystem suitability).

On-Site Salinity Measurements

• Handheld salinity meters: Portable meters used by agricultural experts and water authorities for quick on-site salinity estimates.

• Temperature compensation: Meters commonly self-adjust for temperatures other than $25^{\circ}$C.

• Example: A portable meter reading might show salinity as a certain ppt (parts per thousand) value, e.g., $5$ ppt at $32^{\circ}$C (Figure 16.1.12).

Soil Salinity: 1:5 Weight/Volume Method

• Procedure:
  1) Dry soil sample is weighed; mix 1 part dry soil (g) with 5 parts water (mL). Example: 20 g soil with 100 mL distilled water.
  2) Stir well and allow soil to settle; measure the salinity of the water phase (EC) with a portable salinity probe.
  3) Determine soil salinity by applying a conversion value based on soil texture (Table 16.1.5).

• Soil texture affects conversion: the percentage composition of sand, silt, and clay determines the conversion value.

• Example conversion values (Table 16.1.5):

  • Sandy: 17

  • Silty sand: 14

  • Silty: 10

  • Silty clay: 9

  • Clay: 7

• Soil salinity calculation: $EC{soil} = EC{water} \times conversion\;value$ (for the corresponding soil texture).

Phosphates, Detergents, and Zeolites (Detergents and Water Quality)

• Australian detergents: By 2014, most brands phased out phosphates due to environmental concerns.

• Zeolites: Replacements for phosphates; aluminosilicate minerals with many tiny pores (< 2 nm) and high surface areas; bind Ca$^{2+}$ and Mg$^{2+}$ on their surfaces, removing hardness-causing cations from water.

• Impact: Phosphate-free detergents reduce nutrient loading in waterways; zeolites help soften hard water without introducing phosphates.

Visual Aids and Key Figures (Referenced Concepts)

• Figure 16.1.1: Lake Eyre dry bed showing salt deposits; high salinity as a natural extreme.

• Figure 16.1.2: Limestone formations and cave development through dissolution and redeposition of calcite by rainwater; related to regional mineral deposits.

• Figure 16.1.3: Eutrophication effects from high phosphate levels leading to algae blooms and possible toxic blooms (Nodularia).

• Figure 16.1.4: Relative densities of heavy metals vs. light metals; context for toxicity and environmental persistence.

• Figure 16.1.5: Mercury movement through the food chain; bioaccumulation illustrated across trophic levels (methylmercury example).

• Figure 16.1.6: Structural depiction of tetraethyl lead ($Pb(C2H5)_4$) used in industry and its potential impact on soils and waterways.

• Figure 16.1.7: Minamata disease case – a boy receiving physiotherapy for mercury poisoning effects.

• Figure 16.1.8: Limescale buildup inside pipes due to soap scum precipitation in hard water.

• Figure 16.1.9/16.1.10: Conductivity-based salinity detection circuit; relationship between current/light and ion concentration.

• Figure 16.1.11: Conductivity vs. concentration relationship at low concentrations (linear region).

• Figure 16.1.12: Portable digital salinity meter; shows temperature-compensated reading (e.g., 5 ppt at 32°C).

Case Study and Practical Takeaways

• Minamata disease case study demonstrates the real-world danger of mercury pollution and bioaccumulation in ecosystems and humans.

• Hard water effects are not only chemical but also practical (soap scum, pipe scaling, energy inefficiency).

• Salinity testing via EC is a cornerstone method in water quality assessment; combining EC with temperature control provides robust practical data.

• Soil salinity determination requires texture-based conversion to translate water salinity into an index that reflects plant tolerance and soil conditions.

• Policy and industry shifts (phosphates phase-out, use of zeolites) show how chemistry informs environmental regulations and practical water treatment solutions.

Quick Reference Formulas and Facts (LaTeX)

• Soap–hard water precipitation:
  2C{17}H{35}COO^-(aq) + Ca^{2+}(aq)
  ightarrow Ca(C{17}H{35}COO)_2(s)

• Organometallic example (tetraethyl lead):
  Pb(C2H5)_4

• Methylmercury organometallics:
  CH3Hg^+ ext{ (as methylmercury salts like } CH3HgCl, CH_3HgOH)

• Conductivity-concentration intuition:
  (EC \propto [\text{ions}])

• Soil salinity conversion (example):
  EC{soil} = EC{water} \times \text{conversion value}

• 1:5 soil–water extraction: mix 1 part soil (g) with 5 parts water (mL) (e.g., 20 g soil with 100 mL water).

Key Terms to Know

• Salts, mineral salts, heavy metals, organometallics, hardness, limescale, eutrophication, algal blooms, nodularia, bioaccumulation, methylmercury, Minamata disease, zeolites, hardness precipitation, electrical conductivity (EC), $\mu$S cm$^{-1}$, 25°C standard, 1:5 soil extraction, soil texture conversion values.