Special Project 4 - Control of Temperature Conditions

1. Raise the temperature

1. Promote the hydrolysis of certain ions, such as high-valent metal cations and easily hydrolyzable anions

Exercise 1 Currently, about 80% of the world's new gold mines use oxidation methods to extract gold. The process of recovering gold, silver and other precious metals from zinc smelting slag in a factory is shown in the figure below:

HCN is known to be highly toxic, with Ka(HCN)=5×10-10, Au++2CN- =[Au(CN)2]-equilibrium constant KB=1×1038

In the “cyanation” process, the dissolution rate of gold reaches the maximum value at 80°C, but the temperature of the reaction solution is controlled during production At 10-20℃, the reason is: _______________ (just answer one question).

Answer The increase in temperature promotes the hydrolysis of cyanide and increases the volatilization rate of HCN; as the temperature increases, the solubility of Ca(OH)2 decreases and part of the alkali precipitates from the solution.

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Exercise 2: "The process flow of preparing nickel oxyhydroxide (2NiOOH·H2O) from NiO-containing waste materials (impurities are Fe2O3, ?CaO, ?CuO, etc.)" in a certain chemical plant As shown in the figure:

The figure shows the relationship between the nickel leaching rate and temperature during acid leaching. The appropriate leaching temperature during acid leaching is ____________℃. If the temperature is controlled at about 80℃ during acid leaching, Then filter residue 1 will contain a certain amount of Ni(OH)2, and the reason may be _______________.

Answer 70 As the temperature increases, the degree of Ni2+ hydrolysis increases, thus forming a certain amount of Ni. (OH)2 precipitation

The analysis shows that when the temperature is around 70°C, the leaching rate of nickel is higher, so the suitable temperature for acid leaching is 70°C; Ni2+ can be hydrolyzed to generate Ni(OH) )2. Heating can promote hydrolysis, so the filter residue 1 at around 80°C will contain a certain amount of Ni(OH)2.

Exercise 3 Cuprous chloride is an important chemical product and is commonly used in organic matter. Synthetic catalyst can also be used in pigments, anti-corrosion and other industries. It is insoluble in H2SO4, HNO3 and alcohol, slightly soluble in water, soluble in concentrated hydrochloric acid and ammonia, and is easily hydrolyzed and oxidized into green basic copper chloride in humid air [ Cu2(OH)3Cl]. Using sponge copper (main component is Cu and a small amount of CuO) as raw material, the process of producing CuCl using ammonium nitrate oxidation decomposition technology is as follows:

(1) Wash the precipitated CuCl crystals with water. Wash immediately with absolute ethanol, dry in a vacuum dryer at 70°C for 2 hours, and then cool and seal the package. The reason for vacuum drying at 70°C and sealed packaging is

(2) As shown in the picture. Under the optimal ratio of each reactant, the reaction temperature affects the CuCl yield. It can be seen from the figure that when the solution temperature is controlled at 60°C, the CuCl yield can reach 94%. When the temperature is higher than 65°C, the CuCl yield can reach 94%. will decrease, the reason may be ____________________________________________________________________________

Answer (1) Vacuum drying can speed up the volatilization of ethanol and water, and sealed packaging can prevent CuCl from being hydrolyzed and oxidized in humid air;

(2) Because the yield of CuCl is maximum at 60°C, according to the information, as the temperature increases, the hydrolysis of CuCl is promoted and the oxidation rate of CuCl is accelerated.

The experimental results obtained by practicing the reaction of 4TiO2·xH2O precipitation with hydrogen peroxide and ammonia for 40 minutes are shown in the table below:

Temperature/℃

30

35

40

45

50

TiO2·xH2O conversion rate

92

95

97

93

88

Analyze the reason why the conversion rate of TiO2·xH2O is the highest at 40℃_______________.

Answer: The conversion rate of TiO2? ?xH2O conversion reaction rate decreases?

Analysis: The conversion rate of TiO2?xH2O is the highest at 40℃. Because below 40℃, the TiO2?xH2O conversion reaction rate increases with the increase of temperature. When the temperature exceeds 40℃, hydrogen peroxide decomposes. The escape of ammonia gas leads to a decrease in the conversion reaction rate of TiO2?xH2O.

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2. Promote the equilibrium to move in the endothermic direction

Exercise 1 Molybdenum disulfide is an important solid lubricant and is known as the "King of Advanced Solid Lubricants". A production process for preparing high-purity molybdenum disulfide using low-phase molybdenite (containing impurities such as MoS2, SiO2, and CuFeS2) is shown in the figure:

(4) From the diagram analysis, it can be seen that the reasons for the precipitation of MoS3 The optimal temperature and time selected in the process are___________, and the principle of chemical equilibrium is used to analyze the reason why the yield of MoS3 decreases when the temperature is lower or higher than the optimal temperature_______________________________.

(5) It is a common principle in industrial production to use low-phase raw materials to prepare high-purity products. As shown in the figure, the reaction [Ni(s)+4CO(g)

Answer (4) 40℃, 30min. The temperature is too low, the reaction is MoS42-+2H+

Analysis (4) ) According to the image, the precipitation rate of MoS3 reaches the maximum at 40°C and 30min, so the optimal temperature and time are 40°C and 30min; if the temperature is too low, MoS42-+2H+ will react

(5) [Ni( s)+4CO(g)

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3. Accelerate the reaction rate or dissolution rate

The 2020 new curriculum standard I vanadium has a wide range of uses. In clay vanadium ores, vanadium exists in compounds with +3, +4, and +5 valences, including aluminosilicates of potassium and magnesium, as well as SiO2 and Fe3O4. The following process flow can be used to prepare NH4VO3 from clay vanadium ore.

"Acid oxidation" requires heating because of ____________________________________.

The answer is to speed up the acid leaching and oxidation reaction rate (promote the complete oxidation)

Analysis of "acid leaching oxidation" requires heating. The reason is: increasing the temperature speeds up the acid leaching and oxidation reactions. rate (to promote complete oxidation), so the answer is: speed up the acid leaching and oxidation reaction rate (to promote complete oxidation);

(1) Study the effect of temperature on the removal rate of organic matter during the "degradation" process. The experiment is in Performed in the device shown in Figure 1.

① After reacting at different temperatures for the same time, it was found that when the temperature increased from 60°C to 95°C, the organic matter removal rate increased from 29% to 58%. The possible reason is: the oxidation ability of MnO2 Increases with increasing temperature; ________________________________________.

Answer As the temperature increases, the reaction rate accelerates?

Analysis ① As the temperature increases, the reaction rate accelerates. In the same time, more organic matter reacts, and the removal rate increases.

In the "leaching" step of Exercise 3, the methods that can speed up the leaching rate are ___________ (write any two).

The answer is to crush the olivine tailings, appropriately increase the concentration of hydrochloric acid, appropriately increase the reaction temperature, etc.?

Analyze the methods that can speed up the leaching rate in the "leaching" step There are methods such as crushing olivine tailings, appropriately increasing the concentration of hydrochloric acid, appropriately increasing the reaction temperature, etc.

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4. Gasify raw materials with relatively low boiling points, or reduce the solubility of gases in solutions

Exercise 1 The laboratory uses the device as shown in the figure to simulate the coal-fired flue gas desulfurization experiment:

The study found that the desulfurization efficiency of limestone slurry is affected by pH and temperature. When the coal-fired flue gas flow rate is constant, the relationship between the desulfurization efficiency and the pH of the limestone slurry is as shown in the figure. The desulfurization effect is best when the pH is 5.6, and the limestone slurry

Answer The solubility of limestone decreases, and

From the analysis of the relationship between desulfurization efficiency and limestone slurry pH, it can be seen that the desulfurization effect is best when the pH is 5.6. As the pH increases, the solubility of limestone decreases, and

Exercise 2 uses formic acid and potassium carbonate as raw materials to produce potassium diformate. The experimentally measured effects of reaction conditions on product recovery are as follows:

Table 1 Effect of reaction temperature on product recovery

Reaction temperature ( ℃)

20

30

40

50

60

70

80

Product recovery rate (%)

75.6

78.4

80. 6

82.6

83.1

82.1

73.7

②Actual The best reaction conditions that should be selected when producing potassium diformate are that the reaction temperature should be controlled at ____________℃~____________℃. From Table 1, it can be seen that if the reaction temperature is too high, the reaction recovery rate will decrease. The reason may be _________________________________________.

Answer: The temperature is too high and formic acid volatilizes?

Analysis As can be seen from Table 1, the yield of potassium diformate is higher when the temperature is controlled at 50℃~60℃, but the temperature is too high. , the reaction recovery rate will decrease instead. The reason may be: formic acid is easy to volatilize, and the temperature is too high and the formic acid volatilizes.

In Exercise 3, Fe(OH)2 is prepared using FeSO4 solution and NaOH solution in the laboratory. The device is as shown in the figure. Please answer the following questions:

The distilled water used when preparing NaOH solution usually requires The purpose of boiling is ____________________________.

Answer: Remove dissolved oxygen from water?

Analysis: Ferrous sulfate is easily oxidized and deteriorated. Therefore, when preparing NaOH solution, the oxygen in the solution should be eliminated. It can be removed by heating the solution. Dissolved oxygen.

Exercise 4 Tin tetrachloride is used as a mordant and a chlorination catalyst in organic synthesis. The reaction, device schematic and relevant information and data for preparing tin tetrachloride in the laboratory are as follows:

② Anhydrous tin tetrachloride is a colorless, easy-flowing liquid with a melting point of -33°C and a boiling point of 114.1°C.

The SnCl4 obtained in the experiment is slightly yellow due to the dissolved C12. The method of purifying SnCl4 is ______________.

Answer Heating distillation

Analysis Since the boiling point of SnCl4 is 114.1°C, if the SnCl4 obtained in the experiment is slightly yellow due to dissolved C12, the method to purify SnCl4 is heating distillation.

Exercise 5 The main component of dolomite is CaCO3·MgCO3, which is widely distributed in my country. Calcium and magnesium series products produced from dolomite are widely used. Dolomite is calcined and melted to obtain calcium and magnesium hydroxides, and then carbonized to separate Ca2+ and Mg2+. The carbonization reaction is an exothermic reaction, and the chemical equation is as follows: Ca(OH)2+Mg(OH)2+3CO2

The carbonization temperature is maintained at 50~60°C. High temperature is not conducive to the carbonization reaction because of ____________________ and ____________________. Low temperature is also not conducive to the carbonization reaction because of __________________.

Answer The solubility of carbon dioxide is small; magnesium bicarbonate decomposes and the reaction rate is small.

Analysis: This reaction is an exothermic reaction and is reversible. When the temperature is too high, the equilibrium reverse reaction direction moves, the solubility of carbon dioxide decreases, resulting in weakened separation of calcium and magnesium ions, Mg(HCO3)2 It is easy to decompose. If the temperature is too high, it will decompose. If the temperature is too low, the reaction rate is too small, which will take too long to obtain the product, which is not conducive to the carbonization reaction. Therefore, the answer is: the solubility of carbon dioxide is small and magnesium bicarbonate decomposes; reaction rate smaller.

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5. Remove thermally unstable impurities, such as NH 4 HCO 3 , NH4(CO 3 ) 2 , KMnO 4 , NH 4 C1 and other substances

Exercise 1 The separation and purification of substances is the focus of chemistry. Please follow the following According to the purpose of the experiment, the corresponding operations and experimental devices are selected respectively. The following are operations:

a. Distillation ?b. Crystallization method ?c. Add appropriate amount of water and filter? d. Heating (or burning) ?e. Add appropriate amount of hydrochloric acid and evaporate?f. Extraction and separation ?g. Dispensing h. Sublimation

The following is the experimental device:

(1) Remove sodium carbonate from sodium chloride crystals: ______, ______ (fill in the operation number and experimental device diagram number respectively, the same below) .

(2) Remove sodium chloride from calcium carbonate: _______, ______.

(3) Separate the mixture of acetic acid (boiling point 118°C) and ethyl acetate (boiling point 77.1°C) (the two are mutually soluble): ______, ______.

(4) Extraction of bromine from bromine water: _______, _______.

(5) Remove calcium carbonate from calcium oxide: _______, _______.

(6) Methods of separating solid salt and iodine: _______, _______.

Answer e 2 c 1 a 5 f 4 d 3 h 6

Analysis

(1) If sodium carbonate reacts with hydrochloric acid to form NaCl, add an appropriate amount of hydrochloric acid , can be separated by evaporation, corresponding to device 2, so the answer is e; 2;

(2) Calcium carbonate is insoluble in water, and sodium chloride crystal is soluble in water, so it can be separated by filtration method, corresponding to Device 1, so the answer is c; 1;

(3) The two are mutually soluble, but have different boiling points, so the distillation method is chosen for separation, which corresponds to device 5, so the answer is a; 5;

(4) Bromine is not easily soluble in water but easily soluble in organic solvents, so the extraction and liquid separation methods are selected for separation, which corresponds to device 4, so the answer is f; 4;

(5) Carbonic acid Calcium decomposes at high temperature to generate calcium oxide, then the thermal decomposition method is selected to remove impurities, which corresponds to device 3, so the answer is d; 3;

(6) Iodine is easy to sublime, so the sublimation method is selected to separate solid salt and iodine , corresponding to device 6, so the answer is h; 6.

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2. Lower the temperature

1. Prevent a substance from decomposing (or dissolving) at high temperatures

Exercise 1 The anode mud of electrolytic refining of copper mainly contains precious metals such as Ag and Au. The following is a flow chart for recovering silver and gold from refined copper anode slime:

The reason why "low-temperature roasting" is used instead of "high-temperature roasting" when oxidizing copper anode slime is ____________________.

The answer: During low-temperature roasting, Ag and oxygen are converted into Ag2O. At high temperature, silver oxide decomposes and generates Ag and oxygen. Therefore, the answer is: During high-temperature roasting, the generated Ag2O decomposes into Ag and O2 (or 2Ag2O

A process flow for the wet preparation of phosphoric acid from Beijing Juan phosphate concentrate in Exercise 22018 is as follows:

It is known that the main component of phosphate concentrate is Ca5(PO4)3(OH) , also contains Ca5(PO4)3F and organic carbon, etc. Solubility: Ca5(PO4)3(OH)

(1) H2O2 oxidizes the organic carbon in crude phosphoric acid to CO2. At the same time, it will also decompose itself. The organic carbon removal rate at different temperatures is shown in the figure. The reason for the change in removal rate after 80℃:

The answer diagram shows the organic carbon removal rate at the same feed ratio, the same reaction time, and different temperatures. The reaction rate increases as the temperature increases before 80°C. The same.

Exercise 3: A kind of copper anode mud (mainly The process flow for separating and extracting various metal elements from copper (containing copper, silver, gold, and a small amount of nickel) is as follows:

When "separating copper", if the reaction temperature is too high, there will be obvious gas evolution. The reason is ____________________________.

The answer is that the temperature is too high and H2O2 decomposes to release oxygen.

The main components of Exercise 5 are FeTiO3 (containing a small amount of MgO, SiO2 and other impurities), Li4Ti5O12 and LiFePO4 is an electrode material for lithium-ion batteries and can be prepared using ilmenite. The process flow is as follows:

In process 2, when solid TiO2 reacts with hydrogen peroxide and ammonia to convert into (NH4)2Ti5O15 solution, the Ti element The relationship between the leaching rate and the reaction temperature is shown in Figure 2. When the reaction temperature is too high, the reason why the Ti element leaching rate decreases is ____________________________________________.

Answer: The temperature is too high, and the decomposition of hydrogen peroxide and the escape of ammonia cause the leaching rate of Ti element to decrease.

Exercise 6 Industrially, high-performance magnetic material manganese carbonate (MnCO3) is prepared from pyrolusite (the main component is MnO2, containing a small amount of impurities such as SiO2 and Fe2O3). The industrial process is as follows:

(1) The by-product MnS2O6 is often generated in the "manganese leaching" reaction. The effect of temperature on the "manganese leaching" reaction is shown in the figure on the right. In order to reduce the generation of MnS2O6, " The suitable temperature for "manganese leaching" is ___________________________.

(2) When adding NH4HCO3 solution to the filtrate obtained from filtration II, the temperature should be controlled at 30-35°C. The reason why the temperature should not be too high is ______________________________________________________________________.

Answer (1) 90℃.

(2) The ammonium salt is decomposed by heat. Add ammonium bicarbonate solution to the filtrate obtained by filtration. The reason for controlling the temperature at 30-35°C is to prevent NH4HCO3 from being decomposed by heat and improve the utilization of raw materials;

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2． Move the chemical equilibrium toward the exothermic direction

Exercise 1 Preparation of phenol acetate:

①The possible reasons for using crushed ice cubes instead of water are: ____________________________________.

Answer: This reaction is an exothermic reaction. Low temperature of crushed ice is conducive to the formation of ester?

Analysis ① Low temperature of crushed ice is conducive to the formation of ester, so the answer is: This reaction It is an exothermic reaction, and the low temperature of crushed ice is conducive to the formation of ester.

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3. Liquefy a product with a high boiling point and separate it from other substances

Exercise 1 Graphite has important applications in the field of materials. A certain primary graphite contains impurities such as SiO2 (7.8%), Al2O3 (5.1%), Fe2O3 (3.1%) and MgO (0.5%). The designed purification and comprehensive application process is as follows:

(Note: The boiling point of SiCl4 is 57.6?C, and the boiling points of metal chlorides are both higher than 150?C)

To the reactor Before passing Cl2, N2 needs to be passed for a period of time. After high-temperature reaction, the oxide impurities in graphite are converted into corresponding chlorides. The purpose of condensation at 80°C is: ____________________. ②The chemical reaction equation for obtaining gas II from activated carbon is: ____________________.

Answer: At high temperatures, Si element is converted into SiCl4, iron element is converted into FeCl3, Mg element is converted into MgCl2, and Al element is converted into AlCl3. The boiling point of SiCl4 is 57.6℃, and the boiling points of MgCl2, FeCl3, and AlCl3 are all higher than 150℃, heated to 1500℃, MgCl2, FeCl3, AlCl3, SiCl4 are all converted into gas I, condensed at 80℃, SiCl4 is still a gas, while MgCl2, FeCl3, AlCl3 state is solid, easy to separate from SiCl4.

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4. Reduce the solubility of crystals and reduce losses.

Exercise 1 Lithium carbonate is widely used in chemical industry, metallurgy and other industries. The industrial process for preparing lithium carbonate using spodumene (Li2Al2Si4Ox) is as shown in the figure:

Known: The solubility of lithium carbonate is (g/L)

Temperature

10

20

30

40

50

60

80

100

Li2CO3

1. 54

1. 43

1. 25

1. 17

1. 08

1. 01

0. 72

(1) The sulfation roasting temperature is controlled between 250°C and 300°C, mainly due to __________________________________; the amount of sulfuric acid used in roasting is controlled At about l15% of the theoretical dosage, the side effects of adding too much sulfuric acid are __________________.

(2) "Lithium precipitation" needs to be carried out above 95°C. The main reason is __________________. The mother liquor obtained by filtering lithium carbonate mainly contains sodium sulfate, and may also contain _____________ and ______________.

Answer (1) The sulfation roasting temperature is controlled between 250℃ and 300℃. The main reason is that when the temperature is lower than 250℃, the reaction rate is slower. When the temperature is higher than 300℃, the sulfuric acid volatilizes more; The amount of sulfuric acid used during roasting is controlled at about 115% of the theoretical amount. The side effect of adding too much sulfuric acid is that excess sulfuric acid needs to be removed in the subsequent process, which increases the processing capacity of subsequent impurities and increases the burden of subsequent neutralizing acids.

(2) The higher the temperature, the solubility of lithium carbonate decreases. Reducing the dissolution of lithium carbonate can increase the yield; sodium sulfate does not react in the solution. Sodium carbonate should be used in excess, and a small amount of lithium carbonate will dissolve in the solution. The mother liquor obtained by filtering lithium carbonate mainly contains sodium sulfate, and may also contain sodium carbonate and lithium carbonate. The mother liquor obtained by filtering lithium carbonate mainly contains sodium sulfate, and may also contain sodium carbonate and lithium carbonate. Therefore, "lithium precipitation" needs to be carried out above 95°C. The main reason is that the higher the temperature, the solubility of lithium carbonate decreases, which can increase the yield; the mother liquor obtained by filtering lithium carbonate mainly contains sodium sulfate, and may also contain sodium carbonate and lithium carbonate.

Exercise 2 The main component of a certain waste battery material is lithium cobalt oxide (LiCoO2), and also contains a certain amount of compounds of iron, aluminum, copper and other elements. The recycling process is shown in the figure, and finally it can be obtained Co2O3 and lithium salt.

It is known that CoC2O4·2H2O is slightly soluble in water. Its solubility gradually increases with the increase of temperature, and it can react with excess C2O42- ions to form Co(C2O4)n2(n-1)- And dissolve.

(4) In the process of "precipitating cobalt", the relationship between the amount of (NH4)2C2O4 added (Figure a), the temperature of the precipitation reaction (Figure b) and the precipitation rate of cobalt is as shown in the figure:

① As the ratio of n(C2O42-):N(Co2+) increases, the reason why the precipitation of cobalt first gradually increases and then decreases____________________.

② When the precipitation reaction time is 10 minutes and the temperature is above 50°C, the possible reason why the precipitation rate of cobalt decreases as the temperature increases is _______________________________________________________________________________________________.

Answer ① Excess C2O42- reacts with Co2+ to form Co(C2O4)n2(n-1)- and dissolves ② Its solubility gradually increases as the temperature increases

Analysis ① As the ratio of n(C2O42-):N(Co2+) increases, excess C2O42- reacts with Co2+ to form Co(C2O4)n2(n-1)- and dissolves. The precipitation of cobalt first gradually increases and then decreases. ;

②The precipitation reaction time is 10 minutes, and when the temperature is above 50°C, the solubility gradually increases as the temperature increases.

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5. Reduce energy costs and reduce equipment requirements

Exercise 1 The currently commonly used method for industrial production of soda ash is the "joint alkali production method (Hou's alkali production method)"

The world's earliest industrial soda ash production method The method of producing sodium carbonate is the "Lublan method", and its process is as follows:

Compared with the "Lublan method", one of the advantages of the "joint alkali production method" is __________________.

The answer is high utilization rate of raw materials, low temperature required for reaction, and low energy consumption

According to the analysis process, it can be seen that the Lubulan method uses salt crystals and concentrated sulfuric acid at 600°C to The reaction generates sodium sulfate and hydrogen chloride at 700°C, and then uses C, limestone and sodium sulfate to generate sodium carbonate at 1000°C; Hou Debang developed a joint alkali production method in which ammonia and CO2 are directly introduced into a saturated sodium chloride solution. Obtain ammonium chloride and sodium bicarbonate crystals, and use the decomposition of sodium bicarbonate to obtain soda ash.

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3. Control the temperature (water bath or oil bath temperature control)

1. Prevent a certain substance from decomposing or volatilizing when the temperature is too high

In 2019, the Jiangsu laboratory used industrial waste residue (mainly containing CaSO4·2H2O, and also containing a small amount of SiO2, Al2O3, and Fe2O3) as raw materials to prepare light CaCO3 and (NH4)2SO4 crystal, the experimental process is as follows:

(1) Waste residue leaching is carried out in the device as shown in the figure. Control the reaction temperature at 60~70°C, stir, and react for 3 hours. Excessive temperature will cause the conversion rate of CaSO4 to decrease. The reason is: Keep the temperature, reaction time, reactant and solvent amounts unchanged. What are the operations to improve the conversion rate of CaSO4 in the experiment?

Answer: Because ammonium salts are unstable and easily decompose when heated, so if the temperature is too high, (NH4)2CO3 will decompose, thereby reducing the CaSO4 conversion rate; because the reaction during the leaching process is between solid and solution. Reaction (or transformation with precipitation), keep the temperature, reaction time, reactant and solvent amounts unchanged, increase the CaSO4 conversion rate, that is, increase the reaction rate, combined with the impact of external conditions on the chemical reaction rate, increase the CaSO4 conversion rate during the experiment The operation is to speed up the stirring rate (that is, increase the contact area, speed up the reaction rate, and increase the leaching rate).

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2. Control the dissolution and crystallization of solids

Exercise 12017 New Course Standard Volume 3 Potassium dichromate is an important chemical raw material, generally prepared from chromite. The main component of chromite is FeO·Cr2O3. It also contains impurities such as silicon and aluminum. The preparation process is shown in the figure:

The solubility of the relevant substances is shown in the figure.

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