PDH Engineer     PE PDH
PDH Online

Engineering Design - Precipitation, Coagulation, Flocculation


Quiz Questions

1.Precipitation is a physical-chemical process, in which soluble metals and inorganics are converted to relatively insoluble metal and inorganic salts (precipitates) by the addition of a precipitating agent.
True
False
2. Figure 2-1 is a ____________________________________.
Typical schematic of a metals P/C/F system
Solubility of metal hydroxides and sulfides as a function of pH
3.In a super saturated solution, the product of the molar concentrations of the ions is less than the solubility-product constant.
True
False
4. A chelating agent forms multiple bonds with the metal ion. These bonds essentially form a ring in which the metal ion is held so that it is not free to form an insoluble salt. The “pinchers” of the chelating molecule consist of ligand atoms. Common chelating agents are _____________________.
Ethylenediamine tetraacetic acid
Hydrogen Peroxide
5.In hydroxide precipitation, soluble heavy metal ions are converted to relatively insoluble metal-hydroxide precipitates by adding an alkali-precipitating agent. The most common hydroxide precipitating agents are: Caustic soda (NaOH), Hydrated Lime (Ca (OH)2) & Magnesium Hydroxide (Mg(OH)2).
True
False
6.The advantages of hydroxide precipitation are: Ease of automatic pH control, well proven and accepted in industry & relatively simple operation.
True
False
7. The main disadvantage of magnesium hydroxide is cost, which is approximately three times as much as hydrated lime. In addition, magnesium hydroxide precipitation systems are not as easy to operate as lime or caustic. Because of the slow reaction times, equipment-sizing requirements may prove to be very costly owing to higher retention time requirements.
True
False
8. The Soluble Sulfide Precipitation (SSP) process uses two main precipitating agents ? Sodium sulfide (Na2S) & Sodium hydrosulfide (NaHS).
True
False
9.Calcium sulfide is stable only in the dry, solid form. In aqueous solutions, CaS reacts with water to produce Ca (HS)2 and Ca (OH)2 as follows: 2CaS + 2H20 = Ca (HS)2 + CA(OH)2
True
False
10.Flocculation is the process of bringing together the destabilized or “coagulated” particles to form a larger agglomeration of floc by physical mixing or addition of chemical coagulant aids, or both.
True
False
11. Figure 7-2 represents __________________.
Flocculation
Coagulation
12. __________________ are water-soluble organic polymers that are used as both primary coagulants and coagulant aids.
Polyelectrolytes
Precipitates
13. Figure 11-1 represents the __________________________.
Alternating flow diversion equalization system
Completely mixed fixed flow system
14.Destroying cyanide (CN-) is an important pre-treatment step before metals are removed because cyanide forms complexes with metals and prevents them from precipitating as hydroxides. However, once the cyanide-metal bond is broken, the metal is free to precipitate under the appropriate pH conditions.
True
False
15. _______________ is a sludge blanket unit that combines coagulation, flocculation, and settling in a single unit.
Reactor clarifier
Settling chambers