INTRODUCTION
Aluminum sulfate which is much used in water treatment and other processes, is still an import product in Indonesia.
Demand for this chemical is increasing steadily, especially with the construction and planning of water treatment schemes all over the archipelago. Present and future needs are estimated as follows, for which foreign currency to the amount of $ 45 per ton of alum is required.
| 1963 | 7000 ton | 1967 | 12000 ton | |
|---|---|---|---|---|
| 1964 | 9000 ton | 1968 | 14000 ton | |
| 1965 | 9000 ton | 1969 | 15000 ton | |
| 1966 | 11000 ton | 1970 | 17000 ton | 1). |
Raw materials, needed for the production of aluminum sulfate are available locally, such as bauxite and kaolin as the alumina source, and sulfur deposits for the sulfuric acid production. Several conditions however, have to be fulfilled before production of alum in Indonesia can be realized, most important of which is the availability of high grade sulfur and/or sulfuric acid on the local market 2).
Beforo World War II broke out in the Pacific, experiments uere made to produce alum locally. Laboratory experiments wer€ carried out at the Centra! Bureau for Technical Investigations of tlie Department of Industries usirrg bauxite and spent sulfuric acid from the alkylation plant of the STANVAC oil refinery in Sungai Gerong 3). Further experiments were carried out by the oil company in Sungai Gerong on a larger sca-lc. The alurninum sulfate produced, however, contained a large amount of tar like sub tancos which gavc a dark color to the product. These rendered the product unsuitable for water treatment by giving a taste to the water which made it unpalatable. Since then another experiment rvas carried out by A.J. van Bergen and C.A.A. van der Woude to produce alum from kaolin and technical sulfuric acid at the Laboratory for Testing Materials in Bandung a). It must be regretted thnt the pilot plant stage could not be carried out due to lack of funds. During the Japanese occupation, alunrinum sulfate was produced in Sepandjang at the sulfuric acid plant, and in Sungai Gerong at the oil refinery. Both plants stopped their alum production however, after the war came to an end.
PURPOSE OF INVESTIGATION
Due to the rising demand for aluminnm sulfate for water treatment i)urposes, it is considered necessary that Indonesia becorne self-supporting in the supply of this commodity.
Although lndonesian bauxite deposits are large, the amount of high grade baurite is limited, and it is being exported for the production of aluminum or will in the futurc be consumed in the national aluminum industry.
Bauxite tailing, horvever, is available in great quantities and is being discarded as a waste product of the bauxite mines 5;. It contains a substantial amount of iron, so that digestion with acid will give a product, containing both aluminurn and iron snlfa.tes, each of which is known to have coagLrlating properties.
Purpose of this investigation will be to find out:
Whether from bauxite tailing and sulfuric acid, ferric-a.luninum sulfate can be produced which is suitable as a coagulant in water treatment processes.
PREPARATION OF FERRIC ALUMINUM CAKE.
Bauxite tailing was made available through the courtesy of P.N. Tambang Bauksit Indonesia, Kidjan-e, r'ith the follorving analysis:
| Free moisture | \(1.81^{\circ}/_{\circ}\) |
|---|---|
| Dry basis: Al2O3 | \(34.94^{\circ}/_{\circ}\) |
| \(\mathrm{Fe_2O}_3\) | \(19.45^{\circ}/_{0}\) |
| \({\rm TiO_2}\) | \(1.43^{\circ}/_{\circ}\) |
| \(SiO_2\) | \(22.71^{0}/_{0}\) |
| bound water | \(21.56^{\circ}/_{0}\) |
Laboratory equipment for the production of ferric aluminum cake.
Bauxite tailing (2% excess) was ground to a fineness of minus 100 mesh, and digested with 2.37 parts of 45° Bé sulfuric acid in a three neck flask under controlled heating.
As soon as the exothermic reaction set in, the initial heating was decreased, leaving the reacting mixture at reflux temperatures of 105 — 110°C. A stirrer was provided for getting a smooth reaction throughout the mixture. Samples were taken every half hour after the boiling temperature was reached. After three hours of reaction the mixture was poured into a disk, in which the mass solidified after cooling.
| Ai | naly | sis. |
|---|---|---|
| Sample No. | Reaction Time, hours | Yield of soluble | |||
|---|---|---|---|---|---|
| Total soluble oxides | soluble Fe2O3 | soluble Al2O3 | oxides of total oxides in tailing | ||
| 1 | 0.5 | 10.61% | 4.4()° 0 | 6.21% | 66.2% |
| 2 | 1 | 11.56 | 4.57 | 6.99 | 72.2 |
| 3 | 1.5 | 12.58 | 4.81 | 7.77 | 78.5 |
| 4 | 2 | 14.45 | 4.79 | 9.66 | 90.3 |
| 5 | 2.5 | 14.30 | 4.78 | 9.52 | 89.3 |
| 6 | 3 | 14.80 | 5.03 | 9.77 | 92.3 |
- Note: i the percentages of \(Al_2O_3\) were obtained by subtracting % \(Fe_2O_3\) from % total oxides, and thus actually include any minor quantity of \(TiO_2\)
- ii During the cooling (solidification) period some evaporation of water took place, yielding a cake somewhat less than the amount of slurry (95.4%). For obtaining the analysis of the cake, above percentages, which were based on the amount of slurry, should therefore be divided by 0.954. Total soluble oxides in the final cake then becomes
\[\frac{1}{0.954} \times 14.80\% = 15.51\%\]
JAR TESTS
The ferric aluminum cake obtained was compared with imported aluminum sulfate, commonly used for water treatment in Indonesia, and which contained at least 17% Al<sub>2</sub>O<sub>3</sub>.
These comparisons were carried out by jar tests using different surface waters
The following jar test procedure was used:
- 1 minute of rapid mixing with a speed of 100 rpm
- 10 minutes of slow mixing with a speed of 60 rpm
- 15 minutes of settling followed by decantation and filtration.
After flocculation was finished, every jar was given a Floc Index and the time needed for settling of the flocs was indicated in minutes.
The turbidity of the samples was measured after decantation as well as after filtration.
In the filtered water were also determined: specific electrical conductivity at \(20^{\circ}\) C (\(K_{20}\)), total iron content, color and pH.
Coggulant
Floc Index: 4 Pin Point
6 Fair
8 Good
10 Excellent
Sample I: Surface water from Hydraulic Laboratory, ITB Campus
| Coagulant ppm aluminumsulfate|ppm ferric aluminum cake | ||||||
|---|---|---|---|---|---|---|
| 20/20 | 40/40 | 45/45 | 50/50 | 55/55 | 60/60 | |
| Floc index | 4/4 | 8/8 | 8/8 | 10/10 | 10/10 | 10/10 |
| Settling time (minutes) | 15/15 | 6.2/12.2 | 6.1/6.0 | 6.5/3.4 | 8.1/7.0 | 6.1/7.4 |
| Turbidity af- ter decantation | 6.8/8.5 | 2.4/2.9 | 2.2/2.5 | 3.1/3.2 | 3.2/2.9 | 2.2/2.4 |
| Turbidity after filtration | 6.1/6.5 | 0.9/1.2 | 0.7/0.5 | 0.5/0.7 | 0.6/0.5 | 0.8/0.6 |
| \(K_{20}\) (10-6ohm-1cm-1) | 118/119 | 125/122 | 128/128 | 129/129 | 128/127 | 127/126 |
| ppm Fe (total) | 0.05/0.07 | 0/Traces | 0/0 | 0/0 | 0/Traces | 0/0 |
| Color (Pt-Co scale) | 15/20 | 10/15 | 7.5/10 | 7.5/7.5 | 7.5/7.5 | 7.5/7.5 |
| рН | 6.7/6.8 | 6.6/6.6 | 6.5/6.6 | 6.5/6.5 | 6.4/6.4 | 6.4/6.4 |
Sample II: Tjikapundung river water (from the dam near Djalan Siliwangi)
| Coagulant | |||||||
|---|---|---|---|---|---|---|---|
| ppm aluminumsulfate/ppm ferric aluminum cake | |||||||
| 20/20 | 40/40 | 45/45 | 50/50 | 55/55 | 60/60 | ||
| Floc index | 4/4 | 6/6 | \(8^{-}/8\) | 10-/10 | 10/10 | ||
| Settling time | |||||||
| (minutes) | 15/15 | 13.3/13.4 | 9.3/13.4 | 9.3/9.2 | 9.0/9.0 | 9.4/9.0 | |
| Turbidity after | |||||||
| decantation | 3.1/3.7 | 1.4/1.3 | 1.1/1.1 | 1.0/1.0 | 1.0/1.1 | 1.8/1.3 | |
| Turbidity after | |||||||
| filtration | 1.2/1.5 | 0.6/0.6 | 0.2/0.1 | 0.1/0.1 | 0.2/0.1 | 0.2/0.2 | |
| \(K_{20}\) | |||||||
| (10-6ohm-1cm- | 1) 115/111 | 118/119 | 118/118 | 119/118 | 120/120 | 125/121 | |
| ppm Fe (total) | Traces/0.1 | 0/0 | 0/0 | 0/0 | 0/0 | O/O | |
| Color (Pt-Co scale) | 20/15 | 15/10 | 5/5 | 5/5 | 5/5 | 5/5 | |
| pН | 7.3/7.3 | 7.0/7.0 | 6.9/7.0 | 6.8/6.9 | 6.8/6.8 | 6.8/6.9 | |
| Sample III: Tjik | apundung r | iver water | (from Ke | bon Bibit | ) | ||
| Coagulant | |||||||
| ppm aluminumsulfate/ppm ferric aluminum Cake | ||||||
|---|---|---|---|---|---|---|
| 20/20 | 40/40 | 45/45 | 50/50 | 55/55 | 60/60 | |
| Floc index | 4/4 | 8/6 | 6/8 | 8/10 | 10/10 | 10/10 |
| Settling time (minutes) | 10.5/10.6 | 8.1/10.0 | 8.2/7.4 | 10/5/8.1 | 9.2/8.5 | 7.1/7.1 |
| Turbidity after decantation | 5.4/5.8 | 0.7/1.7 | 1.5/1.2 | 1.4/1.0 | 1.2/1.2 | 0.9/1.0 |
| Turbidity after filtration | 3.1/2.4 | 0.4/0.7 | 0.2/0.2 | 0.5/0.2 | 0.2/0.2 | 0.2/0.2 |
| K20 (10-6ohm-1cm- | ¹) 108/107 | 111/110 | 109/110 | 110/110 | 111/111 | 116/111 |
| ppm Fe (total) | Traces/0.06 | 0/Traces | 0/0 | Traces/0 | Traces/0 | 0/0 |
| Color (Pt-Co scale) | 20/30 | 10/15 | 5/10 | 5/10 | 10/16 | 5/5 |
| pН | 7.2/7.2 | 7.0/7.0 | 6.8/6.7 | 6.7/6.7 | 6.7/6.7 | 6.7/6.7 |
| KMnO4 number | 6.8/7.1 | 4.6/4.7 | 1.9/2.5 | 3.5/2.6 | 3.3/3.0 | 2.6/3.3 |
RESULTS OF JAR TESTS
Almost identical results rvere obtained with the produced ferric aluminum cake as compa.red with aluminnm sulfate, commonly used in Indonesia. Only slight differences occur, which, however, can be neglected.
The high iron content in ferric aluminum sulfate did not influence the quality of thc filtered rvater, if the right dose for coagulation was applied.
SUMMARY:
Three hours digestion of ground bauxite tailing with 45' 86 sulfuric acid easily yields a product with a total soluble oxide content of 15,5o/o (compare l5-I7o/o aiumina content in commercial aluminum sulfate).
By not separating the insolubles (8,1o/o of silica and undissolved oxides) from the soluble sulfates, a cake was obtained which is comparatively easy to break and to dissolve.
As a coagulant in water treatment, ferric aluminum cake compares favorably to imported aluminum sulfate, the insoluble matter in the first bcing removed together rvith precipitated colloidal mattcr from the clarified waters.
ACKNOWLEDGEMENT
Thanks are due to the Management of P.N. Tambang Bauksit Iudonesia for making available the bauxite tailing samples. Also to Mr. Loa Beng Loen for carrying out the cxperiments.