Chemical Cleaning Solutions

A wide variety of standard chemical cleaning solutions are available (Table 7.8). Many proprietary solutions are based on these chemicals. Some are patented or involve patented equipment. Chemical cleaning contractors are the best source of information on standard or patented techniques, (see also industrial cleaning manual, TPC-8 NACE). 

Most chemical cleaning contractors calculate the concentration of chemicals in weight percent, but some use volume percent. The user must be aware of this. For example, a 10 wt% solution of HCl is equivalent to 25 vol% of the normal 30% concentrated HCl. 

Mineral acids are strong scale dissolvers. They include HCl, hydrochloric/ammonium bifluoride (HCI/NH4HF2), sulfamic acid (NHjSOjH), HNO3, phosphoric acid (H3PO4), and H2SO4. 

Organic acids are much weaker. They are often used in combination with other chemicals to complex scales. An advantage of organic acids is that they can be disposed of by incineration. They include formic (HCOOH), hydroxyaceticformic, acetic (CH3COOH), and citric acid. 

FejO (Magnetite or mill scale) 2% hydroxyacetic/formic 65-80°C (150-175 °F) 

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EDTA has been determined in a wide variety of sample matrices by HPLC. These matrices include waste waters, natural waters, sediments, fertilizers, chemical cleaning solutions, radioactive waste solutions, and pharmaceutical preparations. Chinnick reported the separation and identification of EDTA and other aminopolycarboxylic acid sequestrants by a high performance liquid chromatographic (HPLC) method [57]. 

The final 1% or so of sludge remaining will probably have to be removed chemically. Various chemical cleaning solutions are being evalu-... 

Polyamide membranes are also not resistant to the strong oxidizing actions of disinfectants such as hydrogen peroxide and hypochlorite. Acids used to the clean membrane system must be rinsed out thoroughly before application of hypochlorite for disinfection as hypochlorite at low pH can cause corrosion in stainless steel. The pH of the chemical cleaning solution must fall within the tolerable range of pH 1-13 for polysulfone membranes and pH 3-8 for CA membranes (87). 

The tubular element Is the least susceptible to fouling and the easiest to clean. This element is widely used in ultrafiltration applications where the process streams contain suspended solids. The tubular element can be cleaned not only by chemical action but also by mechanical means. A sponge rubber ball is pumped through the tubular element with the chemical cleaning solution to scour the membrane surface. 

The hollow fine fiber element, with the great number of close packed fibers, is an effective filter in itself. Consequently, it is the most easily fouled membrane configuration and requires the most pretreatment. The hollow fine fiber element can be cleaned with chemical cleaning solutions, but it is not amenable to mechanical cleaning. It is also more difficult to clean than the spiral wound element. 

Laboratory Corrosion Testing of Metals in Static Chemical Cleaning Solutions at Temperatures Below 93°C(200 F)... 

A good method for studying passive film formation involves examining polarization curves. ° Theoretical anodic and cathodic polarization curves are shown in Figure 1. As the potential is shifted in the anodic (-I-) direction, the current (corrosion rate) increases. At a critical current density (/cnt), the current drops to a low value—indicating the onset of passivation. With the use of polarization curves, the solution conditions controlling passivation can be determined and described. Polarization curve analysis will be extensively used in the subsequent sections to describe passivation in chemical cleaning solutions. 

Surfactants are added to chemical cleaning solutions to improve their wetting characteristics. They are also used to improve the performance of inhibitors, emulsify oils, improve the characteristics of foaming solvents, and act as detergents in acid and alkali solutions. As with inhibitors, most surfactants are proprietary products. 

Acetate and triacetate are essentially unaffected by dilute solutions of weak acids, but strong mineral acids cause serious degradation. The results of exposure of heat-treated and untreated triacetate taffeta fabrics to various chemical reagents have been reported (9). Acetate and triacetate fibers are not affected by the perchloroethylene dry-cleaning solutions normally used in the United States and Canada. Trichloroethylene, employed to a limited extent in the UK and Europe, softens triacetate. 

Casting of Ti alloys for crowns and bridges is done in investment molds that have been allowed to cool almost to room temperatures after firing. The castings are cleaned in electrolytic solutions or in special chemical polishing solutions that impart a bright smooth surface finish to the casting... 

Application of the de minimis limitation to process streams must also be reviewed. Mixtures containing toxic chemicals can be added to a process or generated within a process. In both cases (assuming reporting thresholds are exceeded) a facility is required to consider and report releases from the process up to the point where the concentration of the chemical falls below the de minimis level. For example, a 10% solution of a listed chemical is mixed Into a formulated cleaning solution, resulting in a final concentration of less than 1%. Releases such as air emissions, from the mixing vessel must be counted, but releases from the finished formulation are not counted because the de minimis exemption applies... 

If a displacement reaction is to take place uniformly, the surface of A/j should be chemically clean initially in addition, a wetting agent may be employed in the plating solution. 

All pipes and fittings are transported to the pickling process in which an overhead crane is used to lower them into an acidic pickle liquor solution that chemically cleans and etches the black oxide surface layer resulting in a clean, rust-resistant pipe. 

All reagents and solvents that are used to prepare the sample for analysis should be ultrapure to prevent contamination of the sample with impurities. Plastic ware should be avoided since these materials may contain ultratrace elements that can be leached into the analyte solutions. Chemically cleaned glassware is recommended for all sample preparation procedures. Liquid samples can be analyzed directly or after dilution when the concentrations are too high. Remember, all analytical errors are multiplied by dilution factors therefore, using atomic spectroscopy to determine high concentrations of elements may be less accurate than classical gravimetric methods. 

Note that some of the reactions indicated by the chart are combinations where the heat generated by diluting a material may cause pressurization of an enclosure. Note also that more information is needed about the chemical composition of the cleaning solution before its compatibility with the other materials can be determined. 

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