Chapter 17
Iron Humate Production, Processing, Properties, and Usage
Downloaded by COLUMBIA UNIV on September 6, 2012 | http://pubs.acs.org Publication Date: July 1, 1997 | doi: 10.1021/bk-1997-0668.ch017
B. E. Rehberg and G. L . Smith IMC Vigoro, 150 Third Street Southwest, Winter Haven, F L 33880
Iron Humate is a controlled release iron product generated by the water treatment industry during the production of potable waterfromhumate rich river water sources. Use of pure iron salts to precipitate these complex color agents provides a new raw material that offers more environmentally sound use options than humates precipitated with aluminium or contaminated iron salts. The raw iron humate filter cake can be processed in different ways to produce a range of controlled release iron products. Dried iron humate is the slowest release iron source but exhibitsfragilephysical characteristics. Reaction of wet or dried humate with different acid-base systems and process equipment improves it's physical quality and modifies the release properties of the iron. This integrated approach of linking water purification to the manufacture of multi-use final products hold promise for future environmental management projects.
Traditionally, colored surface water was clarified with aluminum sulfate (alum) by potable water treatment facilities. This treatment coagulated the colored humâtes and created an aluminum sludge which, after dewatering, was discarded. In the past, the sludge was dumped back into the water source, to the detriment of water quality. Current disposal options include lagoon storage, landfills and discharge into sanitary sewers. Inadequacies in all the disposal techniques has led to increased interest in land application of water treatment sludge. Iron salts have also been used to coagulate humâtes but, too often produced a sludge high in heavy metals due to impurities. Another problem encountered with this potable water treatment method was it generally resulted in a sludge with unnecessarily high concentrations of hydrous metal oxides. These metal hydroxides are strong absorbents of metals and phosphorus and can make these essential nutrients unavailable for plant use. Additionally, excessive iron hydroxide levels impede the humate dewater process which translates into increased processing and handling costs. Such problems do not afford materials well suited to land application. 268
© 1997 American Chemical Society
In Agricultural Uses of By-Products and Wastes; Rechcigl, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
17. REHBERG & SMITH
Iron Humate Production, Processing, and Use
269
Integrated Approach to Water Clarification and Slow Release Iron Production.
Downloaded by COLUMBIA UNIV on September 6, 2012 | http://pubs.acs.org Publication Date: July 1, 1997 | doi: 10.1021/bk-1997-0668.ch017
Existing water treatment processes focus primarily on producing high quality drinking water with little regard for the quality of the resulting sludge. The goal of the integrated water treatment process is to produce both high quality water and raw materials for industry. One example of just such a system is seen in a patent issued for the production of iron humâtesfroma potable water color clarification process (/). There are three critical factors required to assure the goals of clear water and effective iron humate can be met: 1) pure ferric sulfate salt, 2) proper iron-humate stoichiometry, and 3) effective pH control. Production of the Iron Humate Raw Material The coagulant salt (ferric sulfate) is manufactured specifically for water treatmentfroma pure grade of iron ore and virgin sulfuric acid. Raw water is tested at the treatment facility to determine the optimum pH conditions (3.8-5.5) and the proper ferric salt to humate stoichiometry to provide clear water and preferred iron humate. Once these factors are determined, the raw water is adjusted to the prescribed pH. Downstream of the acidification zone the pure iron salt coagulant is added at a rate previously established to maximize clarification and minimize iron hydroxide formation. This solution is sent to a flash mixer for a minimum of 15 seconds, then to aflocculatingmixer for 3 to 10 minutes depending upon the temperature of the water. After the reaction is completed, the iron humate is allowed to settle, separate, and is dewatered to about 20% solids. Thisfiltercake is air dried to 55-65% solids, classified and represents the base form of the raw material iron humate. Chemical Composition of Raw Material Iron Humate. Elemental analysis for the principal components are 16.5 to 19.5% Fe, 35% to 40% organic carbon, and 35% to 45% moisture. The physical character of the iron humate is quitefragile.Particle crush strength values run less than 1-2 lb of force. Additional elements present in this raw material are listed below (Table I). Table L Analysis of Iron Humate for Primary, Secondary, Minors and Metals Component Wt% Component ppm Component Dom f f t i r Phosphorous 1.0-1.5 Magnesium Tin 12.0 180-350 Potassium 0.5-1.0 Manganese 150-280 Lead 4.5 Sulfur as S 0 2.5-3.0 Barium 50-120 Titanium 4.4 Calcium 1.5-2.5 Copper 25-85 Selenium 0.14 Chloride 0.2-0.3 Zinc 15-50 Mercury
