CN-117886347-B - Method for producing polyaluminum chloride and recycling sodium chloride by using sodium tetrachloroaluminate waste salt

Abstract

The invention relates to a method for producing polyaluminum chloride and recycling sodium chloride by using a byproduct of production of methylphosphine dichloride, and relates to the technical field of water treatment agents. The method comprises the steps of crushing bulk mixed salt containing sodium tetrachloroaluminate and sodium chloride, dissolving in water, adding sodium metaaluminate, stirring for reaction, filtering to obtain aluminum hydroxide solid and crude brine solution, adding the aluminum hydroxide solid into water, heating and stirring, dropwise adding hydrochloric acid to adjust pH, curing, adding an adsorbent for filtering to obtain polyaluminum chloride solution, transferring the crude brine into a flocculation precipitation tank, adding an oxidant for oxidizing phosphorus-containing impurities, adding sodium hydroxide for adjusting pH, adding polyaluminum chloride, obtaining primary refined brine after precipitation, and filtering the primary brine to obtain refined brine. The invention realizes circular economy and has the advantages of simple process, cheap and easily available raw materials, safety, environmental protection, high economic benefit and the like.

Inventors

• TIAN YIQUN
• PENG CHUNXUE
• YAO HONG
• LIU SANLIU
• ZHANG WENBIN
• LI CONGYUAN

Assignees

• 湖北泰盛化工有限公司

Dates

Publication Date

20260508

Application Date

20231208

Claims (5)

1. 1. A method for producing polyaluminum chloride and recycling sodium chloride by using sodium tetrachloroaluminate waste salt is characterized in that, The method comprises the following steps: (1) Crushing blocky mixed salt containing sodium tetrachloroaluminate and sodium chloride after methyl dichlorophosphine production; (2) Adding the crushed mixed salt into water for four times to dissolve; (3) Adding sodium metaaluminate, stirring for reaction, and filtering to obtain aluminum hydroxide solid and crude salt aqueous solution; (4) Adding the aluminum hydroxide in the step (3) into water, heating and stirring, dropwise adding hydrochloric acid with the mass fraction of 15%, adding adsorbent activated carbon, wherein the mass ratio of the hydrochloric acid to the sodium tetrachloroaluminate in the step (1) is (0.18-0.25): 1, the reaction temperature is 75-85 ℃, the stirring rotation speed is 50-75 rpm, the reaction time is 2-2.5 h, and filtering to obtain a polyaluminum chloride solution; (5) Transferring the crude brine in the step (3) into a flocculation sedimentation tank, adding an oxidant hydrogen peroxide solution to oxidize phosphine-containing impurities, then adding sodium hydroxide to adjust the pH, then adding a polyaluminum chloride solution, and obtaining primary refined brine after sedimentation is finished; (6) The primary refined brine is treated by an ionic membrane to obtain refined brine; and (3) completing the production of polyaluminum chloride and the recovery of sodium chloride by using the sodium tetrachloroaluminate waste salt.
2. 2. The method for producing polyaluminum chloride and recycling sodium chloride by utilizing sodium tetrachloroaluminate waste salt according to claim 1, wherein the mass ratio of sodium tetrachloroaluminate to water in the step (2) is 1 (1.8-2.2), and sodium tetrachloroaluminate is added into water in batches.
3. 3. The method for producing polyaluminum chloride and recycling sodium chloride by utilizing sodium tetrachloroaluminate waste salt according to claim 1, wherein the mass ratio of sodium metaaluminate to sodium tetrachloroaluminate in the step (3) is (0.1-0.3): 1, the stirring rotation speed is 40-60 rpm, and the reaction time is 1-1.5 h.
4. 4. The method for producing polyaluminum chloride and recovering sodium chloride by utilizing sodium tetrachloroaluminate waste salt according to claim 1, wherein the pH in the step (5) is adjusted to 8-10.
5. 5. The method for producing polyaluminum chloride and recycling sodium chloride by utilizing sodium tetrachloroaluminate waste salt according to claim 1, wherein the solid waste obtained in the step (4) is subjected to innocent treatment and then is subjected to RTO incineration.

Description

Method for producing polyaluminum chloride and recycling sodium chloride by using sodium tetrachloroaluminate waste salt Technical Field The invention relates to the technical field of chemical industry, in particular to a method for producing polyaluminum chloride and recycling sodium chloride by using sodium tetrachloroaluminate waste salt. Background Flocculants are the most commonly used water treatment agents and are capable of polymerizing contaminant particles in water to form large flocks, thereby separating contaminants from the water. At present, flocculants in the market are mainly divided into inorganic flocculants, organic flocculants and microbial flocculants. The organic flocculant has low dosage and high efficiency, but the polymer residue is easy to cause teratogenesis and carcinogenesis, the application range is limited, and the microbial flocculant is not mature at present and has wide application. Polyaluminum chloride (PAC) is a water-soluble inorganic high molecular polymer between Al (OH) 3 and AlCl 3, and has a chemical formula of [ Al 2(OH)nCl6-n]m ]. The water-based high-electric neutralization and bridging agent has the advantages of high electric neutralization and bridging effects on colloid and particulate matters in water, strong removal of micro-toxic substances and heavy metal ions, and the like. As an emerging water purification material, polyaluminium chloride is widely applied to various sewage treatment fields such as domestic water, industrial wastewater and the like. The currently commonly used preparation methods of polyaluminium chloride comprise processes such as a metal aluminum method, an alkali dissolution method, an aluminum chloride method, an aluminum hydroxide method, an aluminum oxide method and the like. The method has the defects of complex process, expensive raw materials, higher energy consumption, high impurity content, high potential safety hazard in the production process and the like. There is a need for a cleaner, safer process for producing polyaluminium chloride. In the process for producing methylphosphine dichloride, a large amount of mixed waste salt of sodium tetra-chloroaluminate and sodium chloride (excessive feeding in the reaction) is generated due to the salting-out reaction of the process design. The sodium tetrachloroaluminate produced is highly exothermic when dissolved in water and the solution is acidic, with a small amount of phosphine-containing waste, resulting in a certain risk and difficult handling. Since the advent of the autocorrelation synthesis technology, sodium tetrachloroaluminate waste salts have been the difficulty that the related industry has to face and be difficult to surmount. Patent CN116022836a discloses a method for recovering sodium tetrachloroaluminate, a method for synthesizing polyaluminum chloride by using sodium tetrachloroaluminate. The method comprises the steps of dissolving sodium tetrachloroaluminate slices in water, obtaining aluminum trichloride solid through dehydration and crystallization, dissolving aluminum trichloride in water, and adding calcium powder for reaction to obtain polyaluminium chloride solution. The process condition is simple, the cost is low, but a large amount of sodium chloride can be carried out by crystallization in dehydration crystallization, the aluminum content of the produced polyaluminum chloride can not reach the national standard due to the addition of calcium powder, the phosphine-containing wastewater in the whole process is not treated, other processes or a third party is still needed for treating the wastewater, and the operation cost is increased. Patent CN112794868a discloses a method for treating sodium tetrachloroaluminate produced in the production process of methyl dichlorophosphine, a method for recovering sodium tetrachloroaluminate by-product. Adding sodium tetrachloroaluminate into a sodium hydroxide solution, stirring, reacting, filtering to obtain aluminum hydroxide solid, washing, drying and roasting the aluminum hydroxide solid to obtain an aluminum oxide product, mixing a washing solution with a first filtrate to obtain a sodium chloride mother solution, and concentrating and crystallizing the mother solution to obtain sodium chloride which is subjected to dissolution, precipitation and membrane treatment to obtain refined brine. The method has low cost and higher atom utilization rate, but the sodium tetrachloroaluminate releases a large amount of heat in the reaction process with sodium hydroxide, the process is difficult to control, and the process needs to be treated at high temperature twice, so that the energy consumption is higher. Disclosure of Invention The invention aims at the technical defects and provides a method for producing polyaluminum chloride and recycling sodium chloride by using sodium tetrachloroaluminate waste salt. The technical scheme of the invention is as follows: (1) Crushing the blocky mixed salt containing sodium tetr