{"id":17870,"date":"2026-04-19T16:07:43","date_gmt":"2026-04-19T10:37:43","guid":{"rendered":"https:\/\/aluminiummagazine.com\/mag\/?p=17870"},"modified":"2026-04-19T16:07:44","modified_gmt":"2026-04-19T10:37:44","slug":"aluminium-sulfate-alum-complete-guide","status":"publish","type":"post","link":"https:\/\/aluminiummagazine.com\/mag\/aluminium\/compounds\/aluminium-sulfate-alum-complete-guide.html","title":{"rendered":"Aluminium Sulfate (Al\u2082(SO\u2084)\u2083): The Complete Guide"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Aluminium sulfate is an important industrial chemical, commonly referred to as &#8220;alum&#8221; (though strictly, alums are double sulfates). It appears as a white crystalline solid that is highly soluble in water. It is the backbone of municipal water treatment, serving as the definitive flocculent that delivers clear drinking water.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">1. <strong>Basic Identification<\/strong><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Chemical Formula:<\/strong> Al\u2082(SO\u2084)\u2083 (anhydrous); common hydrates: Al\u2082(SO\u2084)\u2083\u00b718H\u2082O or Al\u2082(SO\u2084)\u2083\u00b716H\u2082O<\/li>\n\n\n\n<li><strong>Alternative Names:<\/strong> Filter alum, papermaker&#8217;s alum, dialuminum trisulfate<\/li>\n\n\n\n<li><strong>Molecular Weight:<\/strong> 342.15\u202fg\/mol (anhydrous); ~666.4\u202fg\/mol (octadecahydrate)<\/li>\n\n\n\n<li><strong>CAS Number:<\/strong> 10043-01-3 (anhydrous); 7784-31-8 (octadecahydrate)<\/li>\n\n\n\n<li><strong>Appearance:<\/strong> Glossy white crystals, granules, or powder<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">2. <strong>Physical Properties<\/strong><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Property<\/th><th class=\"has-text-align-center\" data-align=\"center\">Aluminium Sulfate (Anhydrous)<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Melting Point<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">770\u202f\u00b0C (1418\u202f\u00b0F) \u2013 decomposes<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Boiling Point<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Decomposes to Al\u2082O\u2083 + SO\u2083<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Density<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">2.67\u202fg\/cm\u00b3<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Aqueous pH<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">2 \u2013 4 (acidic)<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Solubility<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">31.2\u202fg\/100\u202fmL (0\u202f\u00b0C); 86.9\u202fg\/100\u202fmL (100\u202f\u00b0C); insoluble in ethanol<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Aluminum sulfate is a heavy white granular material. It is stable, non\u2011fuming, and non\u2011volatile. It absorbs moisture from air to form hydrates but does so peacefully (no violent reaction).<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">3. <strong>Chemical Behavior &amp; Synthesis<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">3.1 Hydrolysis \u2013 The Coagulation Mechanism<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">In water, Al\u2082(SO\u2084)\u2083 dissociates to Al\u00b3\u207a and SO\u2084\u00b2\u207b. The Al\u00b3\u207a ion hydrolyzes:<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<p class=\"has-large-font-size wp-block-paragraph\"><strong>Al\u00b3\u207a + 3 H\u2082O \u21cc Al(OH)\u2083 \u2193 + 3 H\u207a<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This produces a gelatinous precipitate of aluminum hydroxide that traps suspended particles (flocculation).<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">3.2 Synthesis<\/h3>\n\n\n\n<p class=\"has-large-font-size wp-block-paragraph\"><strong>Al\u2082O\u2083 + 3 H\u2082SO\u2084 \u2192 Al\u2082(SO\u2084)\u2083 + 3 H\u2082O<\/strong><\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">Bauxite or pure alumina is digested in hot concentrated sulfuric acid. The solution is concentrated and crystallized.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">4. <strong>Industrial &amp; Laboratory Applications<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">4.1 Water Purification (Primary Use)<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">As a coagulant, aluminium sulfate neutralizes the negative charge on suspended dirt particles, allowing them to clump into heavy flocs that settle out. This is the standard method for producing clear drinking water from turbid sources.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">4.2 Paper Manufacturing<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Used to \u201csize\u201d paper \u2013 making it resistant to ink bleed. Aluminum sulfate causes rosin sizing agents to bind to paper fibers under acidic conditions.<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<h3 class=\"wp-block-heading\">4.3 pH Regulation in Gardening<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Aluminium sulfate lowers soil pH (makes it acidic). Gardeners use it to turn hydrangea flowers deep blue by freeing natural aluminum in the soil.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">4.4 Antiperspirants &amp; Medical Astringents<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Its astringent properties block sweat glands and stop bleeding from shaving cuts (styptic pencils).<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">5. <strong>Safety &amp; Hazard Management<\/strong><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>GHS Symbol<\/th><th>Meaning<\/th><\/tr><\/thead><tbody><tr><td>\u2757 GHS05<\/td><td>Corrosive<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Critical Warning:<\/strong> Solid is stable, but concentrated aqueous solutions are strongly acidic and can cause burns.<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<h3 class=\"wp-block-heading\">5.1 Health Effects<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Route of Exposure<\/th><th>Effect<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Inhalation<\/strong><\/td><td>Dust causes stinging irritation to nose and throat.<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Skin Contact<\/strong><\/td><td>Prolonged contact leads to drying, irritation, mild acid burns.<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Eye Contact<\/strong><\/td><td>Dangerous \u2013 dust dissolves in eye moisture to form acid, causing severe conjunctivitis and potential tissue damage.<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Ingestion<\/strong><\/td><td>Irritation of mouth\/stomach; sour taste; high doses cause vomiting.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">5.2 PPE<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Respiratory:<\/strong> N95 dust mask (for dry powder)<\/li>\n\n\n\n<li><strong>Hands:<\/strong> Nitrile or rubber gloves<\/li>\n\n\n\n<li><strong>Eyes:<\/strong> Tight\u2011sealing chemical goggles<\/li>\n\n\n\n<li><strong>Body:<\/strong> Lab coat or apron<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">5.3 First Aid<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Eyes:<\/strong> Flush 15\u201120 minutes; seek ophthalmologist<\/li>\n\n\n\n<li><strong>Skin:<\/strong> Wash with soap and water<\/li>\n\n\n\n<li><strong>Ingestion:<\/strong> Drink water or milk to dilute; do not induce vomiting; seek medical attention<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">6. <strong>Storage &amp; Handling<\/strong><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Container:<\/strong> Thick plastic or glass \u2013 <strong>not<\/strong> unlined metal (acidic)<\/li>\n\n\n\n<li><strong>Atmosphere:<\/strong> Keep dry to prevent caking<\/li>\n\n\n\n<li><strong>Location:<\/strong> Well\u2011ventilated, dry storage<\/li>\n\n\n\n<li><strong>Disposal:<\/strong> Dilute and neutralize with lime or soda ash before landfilling<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">7. <strong>Environmental Impact<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Aluminium sulfate can lower pH of water bodies if dumped in large quantities, harming aquatic life. However, controlled doses are used to remove toxic phosphorus blooms (eutrophication) from lakes \u2013 the flocs settle and remove algae\u2011feeding nutrients.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">8. <strong>Comparison with Other Aluminium Compounds<\/strong><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Compound<\/th><th class=\"has-text-align-center\" data-align=\"center\">Formula<\/th><th>Primary Nature<\/th><th>Primary Use<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Aluminium Sulfate<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Al\u2082(SO\u2084)\u2083<\/td><td>Acidic polyatomic salt<\/td><td>Water purification, pH adjustment<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Aluminium Chloride<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">AlCl\u2083<\/td><td>Fuming Lewis acid<\/td><td>Petrochemical catalysis<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Potassium Alum<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">KAl(SO\u2084)\u2082<\/td><td>Double sulfate salt<\/td><td>Pickling, crystal deodorant<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">9. <strong>Frequently Asked Questions<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Q: Is aluminum sulfate the same as the alum block for shaving?<\/strong><br>A: No. Shaving alum blocks are typically potassium alum (KAl(SO\u2084)\u2082). Aluminum sulfate is more acidic and would sting more.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Q: Does this mean I\u2019m drinking aluminum?<\/strong><br>A: No. The aluminum hydroxide floc settles out and is removed. The clarified water contains negligible aluminum.<\/p><div class=\"pai-ad\" style=\"min-height:250px;visibility:hidden;\"><span style=\"display: block; text-align: center; font-size: 10px; margin: 0 0 10px 0; color: #999999;\">Ads<\/span>\r\n<!-- Display-300x250-1 -->\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:inline-block;width:300px;height:250px\"\r\n     data-ad-client=\"ca-pub-3838168351244230\"\r\n     data-ad-slot=\"9933646018\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><\/div>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Q: How fast does it turn hydrangeas blue?<\/strong><br>A: Over a growing season. It lowers soil pH, freeing natural aluminum for root uptake, gradually shifting flowers from pink to blue.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<div style=\"height:75px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">10. <strong>Summary Data Sheet<\/strong><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-center\" data-align=\"center\">Property<\/th><th class=\"has-text-align-center\" data-align=\"center\">Value<\/th><\/tr><\/thead><tbody><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Chemical Name<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Aluminum Sulfate<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Common Name<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Filter Alum<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Formula<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Al\u2082(SO\u2084)\u2083<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Appearance<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">White granules\/powder<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Solubility<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Highly soluble in water (acidic solution)<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Primary Utility<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Water purification coagulant \/ paper sizing<\/td><\/tr><tr><td class=\"has-text-align-center\" data-align=\"center\"><strong>Storage<\/strong><\/td><td class=\"has-text-align-center\" data-align=\"center\">Keep dry to prevent caking<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/p><script>document.addEventListener(\"DOMContentLoaded\",function(){\n        if(window.innerWidth <= 768){\n            if (\"immediate\" === \"delay\") {\n                setTimeout(function(){document.querySelectorAll(\".pai-ad\").forEach(el=>el.style.visibility=\"visible\")},0);\n            } else if (\"immediate\" === \"scroll\") {\n                window.addEventListener(\"scroll\",function(){\n                    let s=window.scrollY\/(document.body.scrollHeight-window.innerHeight);\n                    if(s>0.1){\n                        document.querySelectorAll(\".pai-ad\").forEach(el=>el.style.visibility=\"visible\");\n                    }\n                });\n            } else {\n                document.querySelectorAll(\".pai-ad\").forEach(el=>el.style.visibility=\"visible\");\n            }\n        } else {\n            document.querySelectorAll(\".pai-ad\").forEach(el=>el.remove());\n        }\n    });<\/script>","protected":false},"excerpt":{"rendered":"<p>Aluminium sulfate is an important industrial chemical, commonly referred to as &#8220;alum&#8221; (though strictly, alums are double sulfates). It appears as a white crystalline solid that is highly soluble in water. It is the backbone of municipal water treatment, serving as the definitive flocculent that delivers clear drinking water. 1. Basic Identification 2. Physical Properties &#8230; <a title=\"Aluminium Sulfate (Al\u2082(SO\u2084)\u2083): The Complete Guide\" class=\"read-more\" href=\"https:\/\/aluminiummagazine.com\/mag\/aluminium\/compounds\/aluminium-sulfate-alum-complete-guide.html\" aria-label=\"Read more about Aluminium Sulfate (Al\u2082(SO\u2084)\u2083): The Complete Guide\">Read more<\/a><\/p>\n","protected":false},"author":12,"featured_media":18007,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4155],"tags":[4141,4142],"class_list":["post-17870","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-compounds","tag-aluminium-compounds","tag-aluminum-formula"],"_links":{"self":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/posts\/17870","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/comments?post=17870"}],"version-history":[{"count":0,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/posts\/17870\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/media\/18007"}],"wp:attachment":[{"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/media?parent=17870"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/categories?post=17870"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/aluminiummagazine.com\/mag\/wp-json\/wp\/v2\/tags?post=17870"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}