Aluminium recovery from aluminium foil waste as coagulant for domestic wastewater treatment

The high use of aluminium foil in food and beverage packaging has caused solid waste to increase rapidly, so solid waste treatment is required. This study investigates the best concentration of reactant to aluminium recovery from aluminium foil waste as potash alum coagulant. Potassium hydroxide is used for dissolved aluminium, and sulphuric acid is added to form potash alum crystals. The experimental result got a maximum point for the synthesis of potash alum from aluminium foil: potassium hydroxide 3 M dan sulphuric acid 3 M which produced a potash alum yield’s 99,59% and contains 11,19% of aluminium oxide. The quality of potash alum products is compared to the technical requirements of SNI 0032:2011. Potash alum was applied to the domestic wastewater and compared with commercial alum. The turbidity, TSS, and TDS domestic wastewater treatment results showed that potash alum has better performance than commercial alum.


Introduction
The increasing demand for fast food and household needs for sachet packaging, the more waste generated from this packaging.The most widely used packaging for food is aluminum foil-based packaging because it has the ability to act as an oxygen barrier.[1] To support the circular economic system that the government is promoting in accordance with PP No. 14 of 2015, efforts are being made to utilize this aluminum foil-based packaging waste into something that gives more added value.There have been several studies conducted to process aluminum-based materials into various substances, including alum [2,3], aluminum sulfate alum [4], Poly Aluminium Chloride (PAC) [5][6][7], and aluminum oxide nanoparticles [8].
Besides that, research that turns aluminum into alum can come from a variety of aluminumcontaining raw materials, including aluminum foil and aluminum scrap [3], sachet packaging [2], tetra pack packaging [9,10], and sludge.Waste Water Treatment [11] used cans [12], Lapindo mud [4], and aluminium dross [13].In this research, aluminum recovery was carried out from aluminum foil packaging waste to alum.With so many types of aluminum-based packaging materials, the raw material used in this study was pure aluminum foil packaging because it has the highest aluminum content compared to other food packages.
There has been a lot of research done on turning aluminum waste into alum, but it has only been done to get alum that can be used directly in Waste water treatment processing, it hasn't been compared to the SNI quality standards.for aluminum sulfate, which means that aluminum sulfate, both solid and liquid, that is traded within the territory of the Republic of Indonesia is required to have quality and minimum quality requirements according to SNI 0032:2011 so that it can be commercialized and offer opportunities for the creation of new industries.So that in this study the recovery of solid waste aluminum foil packaging will be carried out into solid alum which has quality requirements according to SNI 0032: 2011, and to see whether the Indonesian National Standard aluminum sulfate SNI 0032: 2015 can be applied to potassium aluminum sulfate alum.
There are several types of alum were made, and in this study, the alum produced was potassium alum.Potassium alum has the chemical formula KAl(SO4)2.12H2Oand is used in water purification, waste treatment, and as a flame retardant.Potassium aluminum sulfate dodecahydrate (potassium alum) is a clear, colorless, transparent crystal with a general shape and well-defined edges.[14] This research will study the optimum conditions for the aluminum recovery process from aluminum foil to solid alum and efforts will be made so that the resulting product meets the quality requirements of SNI 0032:2011, namely by washing and drying the alum crystals.Looking for the process as well as obtaining a comparative performance test of the use of alum produced compared to commercial alum in wastewater treatment.

Material and Methods
The materials used are Aluminium foil sheets which are cut to the size of about 1 cm x 1 cm, Potassium hydroxide, Sulphuric acid, ethanol, and acetone.All the chemicals were purchased from Merck (Germany).Before starting the experiment, we have to prepare the chemical: KOH 1 M; 2M; 3M; 4 M Weigh each KOH of 14 gr, 28 gr, 42 gr, and 56 gr dissolved with distilled water, into a 250 ml volumetric flask up to the tera mark.H2SO4 1 M, 2 M, 3 M, 4 M Pipette each of 14 ml, 28 ml, 42 ml, and 56 ml of sulfuric acid, dissolve it with distilled water in a 250 ml volumetric flask up to the tera mark.
The procedure for making alum from aluminium foil is 1 gram of aluminum foil that has been cut into pieces of 1x1 cm in size is dissolved in 50 ml of KOH and the solution is cooled to room temperature, then filtered using Whatman 41.The filtrate is added to 50 ml of H2SO4 while heating at 80 C and stirring using a magnetic stirrer at 200 rpm until the solution is clear and there are no white lumps.The solution is cooled until aluminate crystals form.
The resulting alum crystals are weighed to determine the product's weight and calculate the yield.The formula used in calculating the yield is as follows: In addition, the analysis carried out is to calculate the Al2O3 content in the alum crystals produced by the titrimetric method based on SNI 0032:2011.Furthermore, the resulting alum was tested for the coagulation process of domestic wastewater compared to commercial alum.The method is domestic wastewater added with alum with a concentration of 500 mg/L for each blank sample, commercial alum, dodecahydrate synthetic alum, and dry synthetic alum.Do fast stirring at 100 rpm for 2 minutes, followed by slow stirring at 40 rpm for 10 minutes.then set aside for 1 hour.The samples were tested for turbidity (nephelometric method), Total suspended solid (gravimetry method, SNI 6989.3:2019), and Total dissolved solid (gravimetry method, SNI 6989.27:2019)levels to determine the coagulation ability of the alum produced.The KOH solution in this study serves to dissolve aluminum from aluminum foil.So the lower the KOH level, the less aluminum is recovered.The chemical reactions that occur are as follows:

Effect of solvent concentration on alum production
Figure 1 shows that the greater the concentration of KOH, the greater the level of aluminum dissolved and recovered into solution, so the alum crystals produced by the addition of 4 M H2SO4 are increasing, this can be seen from the large % yield produced.However, at 3 M and 4 M KOH concentrations, the yield did not show a significant increase, so it can be assumed that at 3 M KOH concentrations, almost all of the aluminum in the aluminum foil has dissolved to form a KAlO2 solution.
Figure 2 shows the high levels of Al2O3 contained in the alum crystals that are formed, where the greater the concentration of KOH, the higher the levels of Al2O3 in the alum crystals, but at the concentration  At a concentration of 1 M H2SO4, the yield of alum crystals was 0, meaning that when added to a solution of 1 M sulfuric acid, alum crystals did not form.To form alum crystals, an excess of sulfuric acid is needed.This is done by the following 2 reactions : The addition of 50 ml of 1 M H2SO4 only formed a white precipitate.This precipitate is aluminum hydroxide, Al(OH)3.Because the amount of sulfuric acid added was less and not excessive, reaction 3 did not occur, so a solution of KAl(SO4)2 was not formed and alum crystals were not formed.The addition of concentrated sulfuric acid is said to be sufficient if the white precipitate of Al(OH)3 is no longer visible in the solution, meaning that all of the K2SO4 solution and the Al(OH)3 precipitate have all reacted with sulfuric acid to form a KAl(SO4)2 solution.When allowed to stand, this KAl(SO4)2 solution will form potash alum crystals.
The highest yield was obtained at around 99% at concentrations of 3 M KOH and 3 M H2SO4, while at 4 M H2SO4, the yield decreased slightly, this was due to a back reaction to K2SO4.The greater the concentration of H2SO4 the smaller the pH value of the solution.The pH value has a significant effect on the rate of crystal growth, this is because the pH of the solution can affect the degree of protonation.The pH of the solution can make the inhibitor molecules more ionized to inhibit the crystal nucleus's growth.[15] Al2O3 levels in the crystals formed showed almost no significant difference in all concentrations of KOH and H2SO4.The Al2O3 content contained in the crystal is around 9 to 11%, still below the minimum requirements of SNI 0032:2015, where the minimum requirement for Al2O3 content is 17%.Taking into account the yield and Al2O3 content, the maximum point for varying concentrations of alum crystal formation was obtained at a KOH concentration of 3 M with an H2SO4 concentration of 3 M, and the yield obtained was 99.59% with an Al2O3 content of 11.19%.The formed potash alum crystals were analyzed quantitatively based on the solid alum quality requirements of SNI 0032:2011.From the results of testing the alum products produced based on the parameters and values of the quality requirements on solid alum SNI 0032:2011 in Table 1, almost all of the parameters for the entrance test are by the specified quality requirements, only the Al2O3 content is still below the quality requirements, so it is necessary to conduct experiments continued so that the Al2O3 content can meet the specified quality requirements.

The effect of ethanol and acetone on Al2O3 content
One of the properties of alum is insoluble in ethanol or acetone so in this experiment we try to wash alum crystal with this solution.Table 2 shows the effect of ethanol and acetone on the alum crystals produced.It can be seen that washing slightly reduces the weight of the crystals, which means that there are impurities that dissolve in ethanol and acetone, thereby increasing the Al2O3 content slightly.The increase in Al2O3 content was not too large, namely around 0.26%, indicating that washing using ethanol or acetone was less effective in increasing Al2O3 levels.However, due to the volatile nature of ethanol and acetone, the washed alum crystals dry quickly.

Variation of drying temperature of alum crystals on Al2O3 content
Based on the chemical reaction that occurs in the formation of potash alum/potassium alum crystals, the product formed has the chemical formula KAl(SO4)2.12H2O.So in the process efforts are made to reduce the water content through heating to increase the Al2O3 content.Table 3 shows that heating at 150 C for 2 hours can remove up to 36% of the water content and the Al2O3 level rises to 17.32% from only 10.16% previously.When heated to a temperature of 150 C and above, the Al2O3 content has entered the quality requirements of SNI 0032: 2011 where the minimum level is 17%.show changes in the shape of alum crystals due to heating at various temperatures.It shows that heating changes the shape of the alum crystals from what was originally a clear crystal clump, due to the increase in temperature it melts and forms a pale white powder.It causes a change in the physical properties of alum crystals, which it's more difficult to dissolve in water.This is by a study conducted by Kishimura where water molecules from KAl(SO4)2.12H2Ocan be removed to become KAl(SO4)2 (anhydrous potassium alum) by heating to 510 K (237 C) for 2 hours.When KAl(SO4)2.12H2O is heated at a temperature of 75 C to 180 C a phase transition occurs from a crystalline to an amorphous phase.[16]

Alum crystal performance test for domestic wastewater coagulation.
The alum crystals formed from the synthesis of aluminum foil need to be compared for their ability as a coagulant with commercial alum.The wastewater used is domestic wastewater, with a coagulant dose of 500 mg/L.Domestic wastewater generally has a turbid color because of solid particles known as colloids that float in solution but cannot precipitate.As colloidal particles are typically negatively charged, the additional ions-such as alum-must be positively charged.In Table 4. Shows a comparison of the analysis value of the use of synthetic coagulants with commercial coagulants based on the turbidity value parameters, Total Dissolved Solid (TDS), and Total Suspended Solid (TSS).The addition of alum coagulant can significantly reduce turbidity and TSS in this domestic wastewater.Commercial alum can reduce turbidity levels up to 89%, TDS 6%, and TSS 82%, while the dodecahydrate synthesized potassium alum can reduce turbidity levels up to 97%, TDS 15%, and TSS 86%.So from the above results, it can be concluded that the ability of potassium alum synthesized from aluminum foil is better than commercial alum.
When the coagulant is added to water, the ions from the coagulant will hydrolyze quickly and form metal hydrolysis, where this cationic metal absorbs into the negatively charged particles, so the particles become neutral.This is the mechanism of the coagulation process.[17] The alum sold in the market is aluminum sulfate dodecahydrate (Al2(SO4)3.12H2O),which forms trivalent aluminum ion Al3+ when added to water.While the synthesized alum is potassium aluminum sulfate dodecahydrate (KAl(SO4)2.12H2O)alum which is a double salt of potassium and aluminum, so when added to water a mixture of 2 separate salts is formed, namely Al 3+ and K + .Therefore the ability of the synthesized potash alum is better than commercial aluminum sulfate alum, this is to the statements of Schultz, 1882 and Hardy, 1900 that the higher the cation charge, the more effectively neutralizes a charged particle.[18] in Figure 9. Shows a visual comparison of initial domestic wastewater with wastewater after adding alum, both commercial alum, dodecahydrate synthetic alum , and dry synthetic alum.Potassium aluminum sulfate which goes through a heating process above 150 C makes the crystal form turn into a fine white powder, not clear lumps like commercial alum, this causes a change in the properties of alum from being easily soluble in water to being difficult to dissolve in water.Therefore when added to wastewater, alum is difficult to dissolve, so it reacts less effectively with ions in water.
The analysis results of dry potassium aluminium sulfate are in Table 4. shows a decrease in turbidity, Total Dissolved Solid (TDS) and Total Suspended Solid (TSS) are smaller than dodecahydrate potash alum, even though the Al2O3 content of dried alum is higher.It does not need a minimum Al2O3 level of 17% to acquire good coagulation abilities, unlike the usage of aluminum sulfate coagulants, because the crystal contains additional K+ ions.The strong coagulating capacity of multivalent ions is primarily not due to their high valence but rather is brought on by their ability to form complexes with water that preferentially adsorb.[19] So it can be concluded that the quality requirements of SNI 0032:2011 only apply to Aluminum sulfate alum types, but do not apply to Potassium aluminum sulfate alum types, because the addition of Potassium metal in alum crystals reduces the Al2O3 content in alum and cannot reach the quality requirements of 17 % in the hydrate form.

Conclusion
Recovery of aluminum from aluminum foil solid waste is capable of producing potassium aluminum sulfate alum that meets the quality requirements of SNI 0032:2011, with the addition of a drying process at 150 C for 2 hours.However, this process resulted in a change in the properties of alum to become difficult to dissolve in water, thus affecting the performance test results for using alum for domestic waste coagulation.The results of the performance tests showed that synthetic potassium alum was better than commercial alum, and dodecahydrate potassium alum had better performance than dried potassium alum.Therefore it can be concluded that the quality requirements of SNI 0032:2011 do not apply to potassium aluminum sulfate alum, especially of Al2O3 content.

4 of 4 M
of KOH (M) 1239 (2023) 012011 IOP Publishing doi:10.1088/1755-1315/1239/1/012011KOH, it shows a decrease in the levels of Al2O3.Figures1 and 2show that the maximum point of aluminum recovery from aluminum foil in KOH solution occurs at a concentration of 3 M.

Figure 9 .
Figure 9. Visual comparison of initial domestic wastewater with wastewater after adding alum, both commercial alum, dodecahydrate, and dry synthetic alum Based on the Regulation of the Minister of Industry No. 67/M-IND/PER/12/2013 concerning the mandatory enforcement of the Indonesian National Standard (SNI) 1239 (2023) 012011

Table 1 .
The results of testing the quality of alum based on the quality requirements of SNI 0032:2011

Table 4 .
The results of the comparative analysis of the use of coagulant types in wastewater