Your smartphone's secret afterlife (Smartphones Unlocked)

A blue mat, a fine-tipped screwdriver, and a dozen itty bitty screws. This is Titus Green's workspace, set within a warehouse that processes 2 million pounds of unwanted electronic waste each year.

Green, 22, and his team at San Francisco Bay Area e-waste collection center Green Citizen, refurbish 30 cell phones a day to put back into customers' hands.

If you don't chuck your electronics down the trash chute (and please don't,) the most likely cycle is that the phone will be refurbished and resold, one way or another.

Of the appliances that come through Green Citizen's doors -- computers, old phones, even an ancient sewing machine -- 21 percent will get a second chance at life. The remaining 79 percent of unwanted cables, motherboards, and TVs are too ancient or too broken for anything beyond tossing individual parts into scrap bins.

Watch this: Four ways to ditch your old electronics

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From there, towering bins containing circuit boards here and batteries there ship out to certified partners that either turn the parts into some other electronic, or smelt metals and other materials out of phones -- like copper or silver, for instance. In addition, certified e-waste recycling centers deal with noxious chemicals in ways that, happily, avoid poisoning people.

Cell phones could kill you
Electronic waste is a huge problem around the globe. The worst-case scenario is that electronic trash winds up in unregulated or mismanaged heaps, slowly leaking corrosive chemicals into the soil and water table.

Nickel, cadmium, mercury, and lead can leach poisons into the earth, taking 20 years or more to decompose.

Let's take lithium for example, the main ingredient in cell phone batteries. It can harm the nervous system and vital organs, according to Green Citizen. Nickel, cadmium, and silver have also been linked to organ damage.

"One cell phone in the trash isn't a big deal," said Steve Manning, CEO of cell phone reseller ReCellular. "100 million in the trash is an environmental disaster."

For a closer look, former CNET reporter Jay Greene investigated the fate of used-up iPhones during a recent trip to China.

Even if you do donate or recycle your phone, there's still a chance that the parts could wind up in this worst-case scenario. Some companies ship parts and whole units abroad, while others prohibit sending e-waste overseas where its use could be unregulated.

The Basel Action Networks' E-Stewards and R2's certification programs are two such examples, and many of the companies I spoke with for this story emphasized that the recycling partners they work with process all electronic parts within the U.S.

The U.S. problem with dumping
Thankfully, e-waste poisoning isn't an issue in most solid-waste landfills in the U.S., according to the Environmental Protection Agency (EPA). But that doesn't let us off the hook.

We still have to consider all the money and energy that goes into manufacturing and shipping brand-new phones across the globe, and digging into the ground for all those copper components in the first place.

Lakes of radioactive chemicals are no joke. These and other toxic horrors are unfortunately still commonplace enough when it comes to obtaining the materials that make a cell phone.

See also: The mines where iPhones are born

The U.S. generates upwards of 2.37 million tons of electronic waste materials each year, according to an EPA 2009 report. To put it into perspective, energy savings from recycling 1 million laptops can power 3,657 U.S. homes, says the EPA.

Small as they are, cell phones make up a significant amount of the total e-waste haul, maybe not in terms of weight, but in terms of volume.

Exact numbers of how many phones are trashed, resold, and recycled are unfortunately hard to come by. Most reports are several years old, but organizations can estimate numbers based on their own data and mathematical models.

The EPA estimates that Americans alone turn over about 130 million cell phones each year, and the number is growing as more people in more households adopt smartphones as their primary communication tool. Cell phones also have shorter lifespans than, say, a computer or a TV, about 18 months on average before owners buy the next hot thing.

However, the good news is that businesses and non-profits are increasingly accepting e-waste like cell phones, from online outfits that will give you money for your old stuff, to certified recyclers like Green Citizen, who will take pretty much anything with a plug, without charging you a drop-off fee.

Yet there's still a long way to go. Globally, we buy 1.7 billion cell phones each year, according to ReCellular CEO Steve Manning. In the US, the figure is closer to 340 million phones sold every year. Only 10 percent-to-12 percent of that quantity make it to a recycling center, and numbers are even lower worldwide says Manning, closer to 9 or 10 percent.

The EPA estimates that for every million cell phones the U.S. recycles, we can recover 35,000 pounds of copper, 772 pounds of silver, 75 pounds of gold, and 33 pounds of palladium -- resources we won't have to dig up fresh from a mine.

Take 2: Back on shelves
So, where do dead cell phones go? The first place you'll see them is back in people's hands. A few phones may get turned into emergency devices to dial 911; these often wind up in shelters serving victims of domestic violence, or in the hands of elderly users.

A much more likely scenario is refurbishment. Whether you donate to a charity, sell your phone online or in a retail store, or drop it off at a recycler, the first order of business for most is to refurbish the phones and sell them back on the thriving secondary market.

Carriers and resellers can give you a cheaper or free refurbished cell phone if you break or lose your original, and independent sellers also stock shelves with these less expensive models.

"You can turn two bad phones into one good phone," said James Kao, Green Citizen's founder and CEO. Green Citizen resells its patched-up handsets to wholesalers and eBay customers.

San Francisco's Green Citizen may only employ 15 technicians to refurbish repairable devices, but they contribute to a roughly $900 million industry for secondary products, according to Kate Pearce, Sr. Strategist and Consultant at Compass Intelligence.

Numbers are conservative and the industry is still undergoing research, but Pearce bases her estimate on 2012's carrier trade-in sales so far for all cell phones and tablets.

Retailers like Best Buy, resellers like EcoATM in the mall, and charities like Cell Phones for Soldiers all pass along the bits and pieces to partners who restore cell phones to working order.

The incentive is twofold. First, why let perfectly good parts go to waste when there's plenty of money to be made? Second, drumming up support from consumers puts unwanted phones in the right hands so they can cycle back through the market and stay out of landfill.

ReCellular is one recycling and resale titan behind many U.S. carriers' recycling and sustainability programs (not to be confused with the trade-ins,) and also picks up recycled cell phones from major stores like Costco and Best Buy. In addition, the company processes all donations made to Cell Phones for Soldiers and Verizon's Hope Line program.

The company's CEO, Steve Manning, says ReCellular can put about 73 percent of the phones it touches back on the secondary market. What it can't sell here in the U.S. through Mobile Karma and other outlets goes to distribution partners in Asia and Latin America.

Believe it or not, the original Motorola Razr is still a big seller in Latin America. "It's built like a tank," Manning said.

What happens to the leftovers?
Phones deemed unfit to remain whole are likely to get dismantled by a recycling facility, with the bits and pieces sold into the commodities market. Nickel, steel, glass, and plastic materials are still valuable, either whole or melted down and turned into something else.

Resources: Sell or donate your cell phone
There are many ways to pass on unwanted cell phones after they've served their purpose, but here are a few resources to get you started.

Online sales or recycling outlets (Including trade-ins)
BuyMyTronics
Swappa
Gazelle
YouRenew
NextWorth
FlipSwap
Cash For Smartphones
Amazon
Target
eBay
Craiglist
Your carrier's buy-back program

Physical sales or recycling outlets
Best Buy
RadioShack
Costco
EcoATM

National charities
Cell Phones for Soldiers
Hope Phones
Hope Line Phones (Verizon)

Local charities
City drives - check with your city government
Local domestic violence centers

What you do with old phones
I was curious about what CNET readers do with their unused cell phones, so I reached out on Twitter, Google+, and Facebook -- do you sell your phones, give them away, donate them?

With a little help from a CNET retweet, I received more than 100 submissions. Some people offered more than one answer, which is fair. For instance, I might sell a high-end device, but may want to hold onto a flip phone for emergencies.

Here's what CNET readers do with their old phones, according to my casual social networking poll.

Of the respondents, 33 use eBay, Craigslist, Gazelle, and Swappa to get cash for old phones, while a relative few (6) said they return old phones to carriers. 37 of you stick old phones in a drawer or closet for backup, for tinkering and testing, or because you plain forget.

Those of you who pass phones on (12) give to organizations benefitting refugees, the elderly, and battered women, while 11 said have taken their handsets to recycling roundups.

Many of you (28) save unwanted cells for your kids, friends, and parents.

Let's not forget the six jokesters who boast getting a kick out eating or dissecting dead phones. Only one respondent claimed to throw old phones in the trash.

What's your personal experience with a cell phone's afterlife? Share them in the comments.

Smartphones Unlocked is a monthly column that dives deep into the inner workings of your trusty smartphone.