lect 14 Flashcards
what are the phase interactions involving water?
what is the size classification of materials in the hydrosphere?
what are sediments?
sediments: layers of finely divided matter covering the bottom of rivers, streams, lakes, oceans, etc
consist of:
-mixtures of clay, slit, sand mixed with organic matter
-vary in composition depending on location and environment
toxins tend to accumulate in ________
SEDIMENTS (e.g. heavy metals and organics)
-danger to aquatic life that spend much time living in/near sediment
-danger to life higher in the food chain
what is the formation of sediments?
what is also considered part of sedimentation?
organic carbon
-biochemical processes such as photosynthesis producing biomass and solid CaCO3, action of anoxic bacteria producing solid FeS
what are some chemical interactions involving solids, gases and water?
what are alternate layers of CaCO3 and FeS in lake sediment?
what is the solubility of solids?
what are colloidal particles in water?
colloidal particles: usually small particles on the size of 1nm to 1um (exhibit tyndall effect)
-size of particles are on the order of wavelength of light (nm scale), causes scattering (slight color)
what is colloidal facilitated transport?
substances that would normally be absorbed to sediments can now be transported through hydrosphere
-e.g. inorganic and organic contaminants, hydrophobic substances
-clays are an important example of colloidal particles in water… due to their cation exchange properties (e.g. heavy metals)
what are the surface properties of colloids?
-surface-to-charge ratio is very high of colloids
-one example of adsorption phenomena
why is the surface-to-charge ratio very high for colloids?
important features of colloids:
-ability to absorb molecules or ions from surrounding solution
-adsorption may be reversible or irreversible
-different purposes: adsorption may bring about decreased concentrations of solutes in water or may facilitate movement of solutes
these aspects will be followed up in a reading for discussion in the coming lectures
what is one example of adsorption phenomena?
-electrostatic attraction to a charged surface
-e.g. clay (aluminum-silicates) have typical negative surfaces
what is ion exchange (replacement)?
what are colloids? what are the types?
-colloid facilitated transport may override binding of contaminants to sediments and offers an alternative transport mechanism
-e.g. clays, humic substances, detergents
-3 types of colloids: i)hydrophilic, ii)hydrophobic, and iii) association colloids (micelles)
-colloidal stability is affected by hydration and surface charge effects
what is the definition of colloids?
-many minerals (clays), some organic pollutants (including humic substances), proteinaceous materials, some algae and some bacteria are suspended in water and wastewater as very small colloidal particles, which are very important in determining the properties and behavior of natural waters and wastewater
-colloids have high surface area/volume ratio contributing to their high surface chemical reactivity, high interfacial energy, and high surface/charge density ratio
what are hydrophilic colloids?
these are macromolecules, such as proteins and synthetic polymers, that are characterized by strong interaction with water, resulting in spontaneous formation of colloids when they are placed in water. Less affected by the addition of salts
-Hydrophilic colloids have functional groups (e.g., –OH, –COOH, –NH₂) that form hydrogen bonds with water molecules, creating a tightly bound layer of water around the colloid particles. This hydration layer acts as a protective shield, preventing the colloid particles from aggregating or coagulating when salt is added.
-Hydrophobic colloids lack a strong hydration layer or steric stabilization, making them more dependent on electrostatic repulsion for stability. When salts reduce this repulsion (by charge screening), hydrophobic colloids are more prone to aggregation and precipitation.
what are hydrophobic colloids?
hydrophobic colloids, such as clay particles, petroleum droplets, and very small gold particles, interact to a lesser extent with water and are stabilized by their positive or negative electrical charges
-tend to undergo settling upon addition of salts
what are association colloids?
consist of special aggregates of ions and molecules called micelles
what are surface properties of colloids?
surface properties of colloids?
