The chemists and engineers at Silver Anvil Engineering have been recovering metals from solutions for the last 45 years. It all started when Roger observed silver bearing fixer being discarded from a photographic lab. He started by recovering silver by using iron replacement with steel wool. Because of the problems of smelting the silver replaced iron wool, he shifted to electro-winning the silver from solution using direct current. Other techniques that were tried included zinc replacement, using proprietary precipitating agents, and ion exchange.
SOLUTION PROCESSING AT SILVER ANVIL CONSISTS OF A NUMBER OR DISTINCT AREAS
- Recovery of silver from photographic and x-ray solutions.
- Recovery of gold and silver from solutions used to strip decorative gold plating from items.
- Recovery of mixed precious metals from solutions.
RECOVERY OF SILVER FROM PHOTOGRAPHIC AND X-RAY SOLUTIONS
The photographic and x-ray process exposes film to light or x-rays: develops the latent image formed in the first step: stops the action of the developer; and fixes the image by removing the unexposed silver halide from the film. All of the solutions used contain enough silver to be classified as “Hazardous” by the Environmental Protection Agency. Silver Anvil specializes in recovering silver from all of these solutions to a level below the 5 ppm (5 milligrams per liter) hazardous level defined by EPA and then disposing of the residual chemistry as a non-hazardous chemical residue. Thus we have cradle to grave control of our chemistry.
Currently we are processing these solutions using the following steps:
(1) Incoming solutions arrive at our plant and are sampled for assay. Volume and pH are recorded and the drum of solution is given a work order number so we can track it through our system.
(2) Incoming fixer is used to strip silver from green or unused film.
(3) The resulting solution is pumped into a holding tank from which it is metered into a set of 6 electrolytic cells in series cascade, followed by a proprietary precipitating agent to take the silver concentration in the fixer from around 2000 parts per million (ppm) to less than 5 ppm. This process takes a hazardous waste solution and converts it to an industrial waste solution for non-hazardous discharge or disposal.
(4) All solutions are pumped into 300 gallon totes, pH is adjusted to more than 5, but less than 9, and samples are taken for analysis by an outside lab to insure that the effluent complies with EPA regulations.
(5) Once the solution in a tote passes it is picked up by a delivery company and taken to non-hazardous solution landfill for ultimate disposal.
RECOVERY OF GOLD AND SILVER FROM CYANIDE BASED SOLUTIONS
The next step was the recovery of other precious metals from cyanide based solutions. Silver Anvil used cyanide based solutions to strip silver and gold from plated items, compact discs and DVDs. The recovery of metals was facilitated by the development of an insitu reaction of the solvent with sulfur dioxide that simultaneously destroyed the cyanide and precipitated the precious metals. EPA officials were so impressed with the closed loop dissolution of precious metals followed by the simultaneous destruction of the cyanide and precipitation of the precious metals that they sent a letter to Silver Anvil that allowed Silver Anvil to use the process without any extra permits. To insure that we were completely legal we obtained a permit from the Adams County Board of Commissioners to store, use, consume and destroy cyanide In our facility. To this day Silver Anvil is the only organization in the Denver Metro Area that is formally permitted to use cyanide solutions to recover precious metals.
We currently reuse cyanide solutions once an accurate analysis is obtained to strip metal from our own products. This is done to consume residual cyanide in solution and make it easier to recover all of the metals in solution.
Today Silver Anvil processes our own solutions which are used to strip silver from plated flatware and film and compact discs and DVDs, as well as gold from computer residue, plated jewelry and other items. In addition we recover precious metals from plating baths and solutions made by others. This includes expired and depleted plating baths as well as baths which have become contaminated by base metals or have become too diluted for practical use.
To process these solutions we receive them in barrels or other containers, record their source and volume, take a pH and then use a coliwasa to extract a representative sample for ASTM gravimetric assay or atomic absorption analysis. All of this information is compiled on a data sheet which defines the recovery and serves as a basis of payment for the customer.
Silver Anvil Engineering has explored processing other solutions that contain precious metal. One of these is Process Water, the aequous solution that is pumped out of the wells with oil. Some oil fields are located near salt domes that contribute salt to the water associated with the oil. This salt often dissolves metals that are also found in the rocks near the oil. Some of these Process Waters have been shown to contain gold, silver, and platinum group metals as well as some base metals. These solutions are processed using a Scott Powell electrolytic coalescing cell that precipitates metals out in an iron matrix from which the precious metals can be extracted.
The Scott Powell cell works well with dilute solutions. When more concentrated solutions are found, they are electrowon with a Reno Cell.
PHOTO OF RENO CELL (COMING)
Metal recovery from solution can be a complicated process. Sometimes the solution has to be treated in a number of steps before the metal can be recovered. Silver Anvil uses a number of techniques depending on the metal to be recovered and its concentration. These techniques include: pH change to precipitate a metal, metallic replacement with a more active metal, electro winning, electro coalescing, use of precipitating agents, ion exchange and other techniques. This work includes the removal of metals to generate a cash flow for our customers, or the removal of trace metals to comply with environmental discharge regulations.
HOW CAN WE ASSIST YOU TO RECOVER METAL FROM SOLUTION ?